The factory mags do suck. I put the kids in mdt lss chassis and the mag release on those are so heavy no kid could drop a mag where as the factory set could barely keep a mag in. I often wish gun company employees actually used what they put out. Often close but still miles away on what really works. The lss is too short in the forarm to really shoot well other than off a bipod but they always have a carbon fiber bipod on it. It's ok from a bench but leaves a lot to be desired from field positions.
I'm going to convert the grendel and the 7.62x39 both to these jeffy bdls and get those carbon fiber stocks this year. Then the 11 and 9 and 7 year old are going to work on shooting from field positions. The lss and bipod were just too frustrating for them in the field. They'd be ok for hunting from a stand or something but they sucked when things were in the field and happening fast.
Bb
I used an MDT LSS on a M7 .223AI with my kids for a while. It worked really well for us off of bags and in fixed position where a rest was available (mainly shooting houses). As you mentioned, off hand with one wasn't the best, especially for a kid....but at that age I didn't want them shooting off hand regardless of platform. Bolt manipulation suffered a bit as well but again, I was ok with slower work there for them at the time. The 5 round mags were good for feeding/keeping up with rounds/easy of unloading, and the release on the M7 version wasn't a problem for the kids. With a thin grip, adjustable stock, and low mounted scope, it had a lot of pro's for a kid...and they were enough to outweigh the cons at that age for the specified use.
Youngest played with a few different rifles last year and left the chassis behind for hunting. He is currently playing with a couple of mini's with me. He's tall enough now the LOP works for him. Definitely a lot better offhand. He's loving it and I think it's a better mousetrap all the way around that the MDT LSS for hunting at his age.