As far as I can see there have been a lot of comments here comparing these cams to C4's, while only looking at the single axle models. I've climbed a bunch with both kouba & c4 cams over the past couple of years and my opinion on the cams varies based on the models.
Single axle (flex, manta etc)
These have been dissected pretty well already. Cheap, not that light, but basic & durable construction. I'll keep climbing on mine in the future, but I wouldn't get more in the generally used c4 ranges (#0.5 to #4). This is more to do with preferring dual axle cams than anything being wrong with these.
What I really like about these is the pricing in the extremes of the size range. I just couldn't justify spending 100€ on a c4 #5 or however much a #0.2 would have cost me. Instead I bought a flex 0.25 for ~30€ and a manta 7 for ~45€. The big manta is actually lighter than a bd #5, while having similar range. I don't mind them being a bit more clunky than other models, as I don't climb hard enough for the cams to be a limiting factor.
If one is concerned about saving weight & money, then the flex cams are sold without a thumb loop as rock empire comets.
Double axle (axel cams)
So far I've bought more of these several times. They are the main cams on my rack in addition to some c4's. I like that they size a bit offset from the c4's, so I have options to find a good placement eg. in between a c4 #1 and #2.
The axle cams have a bit longer stem than bd cams and have an extendable sling, which is nice. Me and friends have fallen on these a bunch, and all are still in good condition. The trigger action got a bit crusty after a couple of seasons, but lubing them up restored them to feel pretty much like new. I guess it's the same with any cam, as over time dirt accumulates near the spring assembly.