Here is my take on piston AR's. Right now htere is not a standard for piston AR's. So replacement parts may not be available or they may be difficult to get. Compatability may be an issue.

Piston AR's are a solution looking for a problem for the majority of people. If you are firing a whole lot of ammo in a short amount of time in an extremely dusty environment pistons have a slight advantage. (Think shooting in Talcum powder) They are cleaner but there are several AR's that are DI that have 50,000 rounds through them with no cleaning and are running just fine.

Like many things. Lubrication is the key to everything. You don't run a working gun dry. It needs a good lubricant in sufficient quantity and there won't be a problem.