By the time you start using bosu balls and other shit you may as well not be lifting weights.
If you want to train your balance, then train your balance. If you want to build your legs, then do something that builds your legs. When you start throwing two conflicting things together you're not doing yourself any favours.
I'm not saying RTC is doing this, clearly he's trying to find ways that hit his legs without back issues and goblet squats/rack position will involve a decent amount of balance. But putting bosu balls in the mix is just going to reduce the weight that can be used to the point where may as well not even be holding a fucking weight in the first place.
edit: I didn't mean this to come off as a rant directed at you KingJulien, fwiw. My point is that some things should stay separate and too many people try and put too many goals into their basket instead of focusing on one at a time.