Overall, they are Ok, but important to know limitations...
During a solo of the Prow V 5.6 C2+, I had a master cam blow
Later on I realized the fault. The placement was directionalized upwards, and when I put my weight onto the piece, the stem bent and it released the lobes. The piece didn't pull because it was a bad placement, it blew because when you bend the stem of a mastercam, the "wires" which attach the lobes of the cam to the trigger come taught and release the upper lobes. This causes the placement to rotate and perhaps pull. Grab one in a store and see for yourself.
****This also happens in horizontal placements.
A true design flaw. But then again, if you are looking to free climb and you aren't going to place these in horizontal cracks, they are mostly bomber. The metal is hard and woln't wear out quickly like aliens, which is nice if you are freeing, good and bad if you are into aid. Like aliens, the flexible stem can get in places that a C3 may not.
If you don't trust CCH/aliens, they are an alternative if you want the flexible stem. I still prefer the rigid C3s for freeclimbing.