i've owned a beta C for about 8 years now & never had any problems what so ever out of it...maybe shot 13000 rds w/it.
i'd just rather use the 20/30 rounders,so i dont get carried away in 100rd mag dumps
As for the knock-off betas,90rd snail drums,ect..i dont know of anyone that has used them.
Armatec makes a very nice 150rd dual drum mag for the ar dont know if they make any in 7.62x51?...though to me the beta is heavy enough w/100rds