It appears that there are several products under this name, a general-purpose solvent/protectant and a dedicated bike chain lube.
Reviews on Amazon are rather mixed...
One fellow claims no better than WD-40, others appear to like it.
Chain lubes are always controversial and seldom tested in a rigorous manner.
WD-40 is essentially a cleaner/solvent and has no more lubricating ability than say...Kerosene.
The best chain lube I ever tried is sadly not being made any more...
Schwinn Factory Wax.
Clean-running, persistent, and according to testing by Bicycling magazine, among the top for wear and abrasion resistance.
To my way of thinking, keeping the chain clean and free of built-up crud and goo is as/more important than what sort of lube used.
bicycles.stackexchange.com/users/1297/M. Werner
Don't bother with spray lube.
It takes only seconds to apply lube from a drip container.
I highly recommend ProGold .
Spraying on lube makes a mess, gets lube on the outer plates of your chain (where it will just collect dirt and grime), and is wasteful to boot.
Just prop your bike up, turn the drip container upside down, touch it to a link, apply a little pressure, and rotate your cranks backward at a medium speed.
You might want to start slowly at first, but eventually you get a feel for how quickly lube gets sucked into the chain.
I don't bother counting links, I just take a quick glance to make sure the links about to go under the bottle are already lubed.
Spin the cranks a bit to make sure the lube works its way into the links, and finally grab the chain with a used rag and spin the cranks until the rag stops collecting dirt.
I squeeze the sides of the plates and get them, then I do it again for the tops and bottoms.
Total time is maybe a minute and a half, and an $8 bottle of lube lasts me for months of weekly application.
bicycles.stackexchange.com/users/1442/Stephen Touset
There is a lab in the U.S.-- Friction Facts -- which publishes a variety of cycling-oriented reports, designed to help riders of all kinds.
Their basic premise is that many small improvements in efficiency are collectively significant.
One of their reports is concerning the best chain lube; a summary of this ran back in 2013 in Velo News .
Unfortunately, I am unaware of any free version of this available on the Web; however, you can download the whole series of reports from Friction Facts for $15 U.S./£10.
That said, I am not a shill for Friction Facts.
In a nutshell, what they showed in their testing was that the best chain lubes are wax-based: regular parrafin wax, Molten Speed Wax , Squirt Lube , and so forth.
Their test showed that the amount of energy lost to chain friction can be greatly affected by lube choice; there is roughly 3.7 Watts of difference between the best and worst lubes in their test.
While it isn't something you're likely to notice on a practical level-- just using a wax lube won't take someone from zero to hero-- for an average rider, who can output an average of 150 Watts for a long ride, it works out to be about a 2.7% improvement.
Collectively, were you to follow all of their recommendations (regarding chain lube, specific chain, pedal, derailleur pulleys, and so forth), they suggest that these improvements will collectively deliver about a 20 Watt savings, which is pretty significant.
But I am not a professional racer, and I ride mainly for fitness,
so I don't mind some losses due to drivetrain inefficiencies, and if a particular lube delivered extra chain life, I might consider it, even if it was not as efficient as some.
BTW, I'm writing from the U.S., and have no idea what GT85 is.
bicycles.stackexchange.com/users/3985/Zippy The Pinhead
I've used GT85 on chains and general bike use for years.
Unlike WD40 it is loaded with PTFE (Teflon) so does have some lubrication properties
but they are very small.
As far as I'm aware it should be treated like WD40 primarily as a water dispersant after cleaning or wet weather riding.
I always supplement it with proper chain lube (either dry or wet depending on the bike and conditions).
bicycles.stackexchange.com/users/147/davefiddes
I am sure WD40 lubricates sufficiently if its present in clean lab conditions, however it does not stick very well and any quantity applied is really thin so will not hang around very long.
From a chain grease you want it to stay between the rubbing surfaces and continue lubricating.
You also want it blocking as much dirt from contaminating the contact surfaces sealing them from contamination which WD40 or other thin oil will never do.
WD40/GT85 and other thin oil will wash off in rainy wet conditions, and not lubricate or protect the chain for very long.
Something thicker is going to be better, also keep in mind that a road bike will work well with a thinner oil/grease then some off road bike being cycled through a swamp.
bicycles.stackexchange.com/users/770/user770
Bike Parts USA have it for sale on their website where they describe it as: Ozone friendly Excellent chain and cable lubricant Stops Oxidation, rust and salt corrosion on metals (sic) surfaces
Loosens rusted or corroded nuts and bolts
So if it isn't any good for your chain somebody better tell them.
bicycles.stackexchange.com/users/79/Amos
I remember a bike magazine in UK recommending GT85 (its a glorified WD40, with the addition of Teflon in it) and they got slammed as the stuff was just not up to scratch, especially for Mountain Bikes.
My answer to this question would be no, dont use it.
I dont have a source for this, happened about 7yrs ago./
bicycles.stackexchange.com/users/316/Simon
GT85 is useful on outdoor bikes.
I wouldn't use it on the chain of my decent bike
but I also have a bike kept outdoors in a rather wet city, with limited space to store spares etc.
and no chance to clean it except a while with a rag.
As even the sprockets are steel on this bike, something that gives an even coating of oil is worth having.
It does seem to stay on the parts long term, unlike WD40.
It also helps with the sticky shifters on the same bike.
So for a good, specialist bike, use good, specialist products, suitable for the conditions.
For something low performance and cheap, any oil is better than none.
bicycles.stackexchange.com/users/7309/Chris H
I've been told by various sources that  WD40 is bad for your chain  so have avoided using it. I've seen people using GT85 on their chains but I'm not really sure how the two products differ. So my question is, should GT85 be used on your chain? Or, does it have the same damaging effects as WD40?
Should you use GT85 on your chain?
bicycles.stackexchange.com
<chain><lubricant>
bicycles.stackexchange.com/questions/3579
bicycles.stackexchange.com/users/446/Phil Hale
Chain lubes are always controversial and seldom tested in a rigorous manner.     The reviews for GT85 on Amazon are mixed. Some people like it others do not.  GT85 has several products, some specifically marketed as bike lube. They are not well tested, but it can be assumed that the spray works better than WD40 due to the added PTFE. These sprays are primarily for cleaning and water displacement, and are too light to last for long in a chain. However, on a cheap bike they are convenient and better than nothing. It would be better to use lube after though.
There are several products with this name, with mixed reviews and without thorough testing. WD40 is primarily for cleaning and water displacement, and should be supplemented with proper lubricant. It is better than nothing though, and GT85 is better still due to the added PTFE, but it is too thin for long term use.