I found that my corner weights would change due to tweak when using the velcro strap. Putting the strap on loose enough to not cause tweak resulted in my lipo popping out. I still use the plastic holders, but use a 1mm carbon fiber strap and a pair of standoffs to hold the lipo in now. No more tweak from the strap. I also found that the strap mind of got in the way when working on the car.
OK, now I see. I use the Tuning Haus lipo retainers on my Schumacher Mi5 as I hate using battery tape. I run my R1 in club VTA races and haven't had any issues with tweek in this class.