I have three Canon CP-E4s and one super cheap "Shoot" brand clone.
Main difference is that the battery compartment door for the clone is a much tighter fit. I have to really push it down to get it to fit. Not a major deal but kind of a pain. The construction on the clone is definitely cheaper overall.
I have two big concerns with the clone, but only time will tell if they are legitimate.
1) I don't have 100% confidence it is always providing power to the strobe. There is really no way to know for sure I guess except by directly comparing the recycle and battery life of the two and I haven't yet done that. It seems to work fine, but really, how do you know?
2) Durability. The weak link in all these packs is the power cord. If it breaks or shorts out, you've got nothing. That's something that will become apparent only over time. I suppose someone might take a knife to the cords to see if the CP-E4 uses better wiring. But then you have a dead battery pack so I'm not going to do that. The only other way to find out is to use them for a while and see if the cords break.
I know this isn't much help. But here is my opinion: If you are using it for paying work, buy the Canon since it's not that expensive – $150 at Adorama. If you are a hobbyist and the battery pack's failure is not going to ruin a job for you, go ahead and get a clone, try it and see what you think. Don't buy multiples of either one until you've bought one and tested it out and decided for yourself.