Old post brought back to life.
I have a couple different brands of piston driven Modern Sporting Rifles in different calibers (5.56/223 & 308/762x51) and have had zero issues with any of them. ALL are great shooters. BCG runs cleaner because you're not dumping the gasses in the bolt to make it function like the DI models.
BIGGEST issue is, they (piston driven), are proprietary to their manufacture. None have interchangeable parts in the gas operation of the weapon and "can" be hard to come by, unlike the DI models.
Other issues. Some brands have been short lived. Thus, making parts even harder to come by if needed. Not much (if any) aftermarket parts to be had. For some reason, the manufactures are very reluctant to send out parts and want the weapon sent in for repairs.