The main difference is in the reversal of these two types of neuromuscular-blocking drugs. 
* Non-depolarizing blockers are reversed by acetylcholinesterase inhibitor drugs since non-depolarizing blockers are competitive antagonists at the ACh receptor so can be reversed by increases in ACh.
* The depolarizing blockers already have ACh-like actions, so these agents have prolonged effect under the influence of acetylcholinesterase inhibitors. Administration of depolarizing blockers initially produces fasciculations (a sudden twitch just before paralysis occurs). This is due to depolarization of the muscle. Also, post-operative pain is associated with depolarizing blockers.
The tetanic fade is the failure of muscles to maintain a fused tetany at sufficiently high frequencies of electrical stimulation. 
* Non-depolarizing blockers have this effect on patients, probably by an effect on presynaptic receptors.
* Depolarizing blockers do not cause the tetanic fade. However, a clinically similar manifestation called Phase II block occurs with repeated doses of suxamethonium.
This discrepancy is diagnostically useful in case of intoxication of an unknown neuromuscular-blocking drug.