I have shot a HK MR556 (civi 416) and the Tavor next to my BCM HSP Jack Carbine... I still prefer my Jack.. and as my name will say... I am an HK fan boy.
Piston costs too much for what you really get out of it...which the only benefit is an extra 3 mins of your less that would usually be spent cleaning your DI system. Sorry but that's about it. They run cleaner.. but not as clean as some people make them out to believe. Also if you throw a suppressor on the gun.. it will run just as dirty as a DI system because the bolt will be unlocking while the can is still under pressure so you will get blow back down the barrel not just a gas tube.
The late great Noveske himself explained this in an older interview of why they toyed around with, but never felt the need to make a piston AR.
Buy what you like, but a piston isn't any more reliable than a DI.. just saves you some time cleaning.. if your time is worth the price difference.. or you just LIKE that particular AR... more power to you.
Have a pic of the Jack and the Tavor.... not the Hk however....