Advocacy for M4 pistons has gone on for years, yet remains but a minor upgrade for the uptight. A marginal improvement, again (like most AR improvements) a minor benefit for those in particular need of it, but otherwise irrelevant - if not problematic - for most users.
I don’t recall details offhand, but have seen critical respectable reviews grudgingly deem AR pistons more trouble (albeit minor) than it’s worth: greater weight, [sometimes] undesirable change in balance/feel, an unintended change to a system designed for direct gas impingement. Keep it reasonably clean, and the gas tube will function fine.
It may be a fine improvement for those articulating (or just desiring) the change, but not worth being a general-purpose ubiquitous modification. Most compelling benefit: attaching a suppressor causes significant increase in gas pressure, getting far more blasted into the operator’s face (gack blarg snort), which a piston can eliminate. Most compelling dissuader: it’s yet another moving part under pressure, just one more thing that can and will break.
The biggest thing about gas pistons is that recoil lift they give off. The beauty of the AR-15 platform is the ability to shoot and pretty much keep the sights on target. The AK suffers from that recoil lift too.
Pistons have weight in the piston that causes the rifle to jump when fired just like an AK-47. I prefer the original gas actuation without that nasty jumping and loss of sight picture.