I bought the CA MP5 midcaps and they worked perfectly (in a TM gun). However, the pins in them came loose after a season and I had to glue the pins in. Not sure if the CA lowcaps will have the same issue. Still, for the price, the CA mags get my recommendation.
For MP5s if you want top of the line you should buy:
lowcaps - TM
midcaps - G&P
highcaps - none