I had one on my carbine. Felt heavier than the KAC FF that's on it now. The rails were also out of spec. The radius of the tube was too big so the rails were essentially too short. I talked with C-More about this problem and they said they were aware of it on the first batch but had fixed it in the second batch. They said they tried a large variety of accessories on their RAS and only found a few that didn't fit. I was lucky enough to have 2 things that didn't fit. One was a KAC vertical grip that I had to file down and the other was a HK ULT light adaptor. I asked if they would replace my unit (I'd had it about a year) but they would not. Needless to say, I won't be buying any of their products ever again.
If you're just screwing around, any of the low end RAS will do the job. If you're serious about your gear (even if you're a chairborne commando like me), spend the extra $$$ can get the KAC, DD or ARMS SIR. You will not be disappointed.