The CASV can hold minis...but some makes are tight if you have a thick solid barrel in there. Little lipo battery would probably fit.
The KA CASV is solid as a rock. Quality made...and you pay for it. The new model with the flip up front sight is really nice.
A lot of "free float"/ris/ras grips are made out of aluminum...some CASV's are made out of heavy guage plate. Fit, finish and market demand make the price. Personally, I like a lot of Madbull's stuff.
No sure what Madbull "CQBR" you're talking about...link or reference helps (madbull makes at lot of different foregrips). But in most CQBR RIS rails...you cannot squeeze any battery in there...so it's either re-wire to the stock or PEQ box.
The term CQBR tends to describe a 10.5" barrel M4, lots of times with RIS foregrip and collapsible stock.