Question: Can I tell by looking through the viewfinder? Well, funnily enough, not necessarily! In theory a pentamirror is darker but design improve all the time and a good pentamirror may out perform a bad pentaprism.
Dell Unveils its Lightest, Smallest and Most Power-Efficient Entry-level Thin Client - Wyse 3040 -- Industry's first entry-level Intel x86 quad-core thin client designed for light multitasking in virtual desktop environments -- Designed for efficiency with 30 percent better performance than previous generations -- Robust connectivity options with superb performance and dual high-definition DisplayPort interfaces PR Newswire ROUND ROCK, Texas, March 29, 2017 ROUND ROCK, Texas ...
You can also, for instance, keep say 100 Citrix servers in a data center and roll out 'thin clients' to 2500+ people around the globe. The servers are then kept secure and safe (since that's where the data is), and the client PCs have nothing to them.