Just bought it. RE, power klaw has no fast attack. Power fist does. Power Klaw cannot clang fast attacks. Power Klaw does more damage against vehicles. It is very, very clumsy and dangerous to use around eldar with all the scorpions, warlocks and banshees spinning around. However it does power through guards and krump hard. Is it good? Not really. It's taken the brunt end of the latest power fist nerfs.
The sprint attack is your best bet but it often messes up and doesn't fire correctly so you end up failing hard in melee. It is absolutely useless against swords unless you attack, hit and kill in one hit. Otherwise you're dead.
It's not useless against A sword. I beat a banshee with it by pounding through her clang, rolling away from her D-bash. Stunned her and iced her. The problem is if you're fighting multiple enemies. It's just so slow and eldar are so fast that when a warlock comes flying at your ass with a power sword through the back or you get back sliced by a scorpion chainsword, you're basically done before the windup goes through. So it's okay in duels, I just wouldn't want to be breaching a room with a power klaw. You'd get surrounded and massacred.
I want to see a video of this, I've had many duels and sword users have always sliced me up before I can get an attack off. It is way, way, way too slow. Surely you clanged once with the banshee, then she proceeded to destroy you while you tried to get another attack off? Or rolled when your attack finally fired so you did 0 damage then you're dead? This is a duel with the Klaw against a sword user. Beating one banshee does not a useful weapon make. Play with it more, I found it extremely lacklustre.