Yep, the horse be dead, long live the horse.
Note that when we talk of "gas piston systems" for AR-type rifles, we are gathering a number of disparate principles under the tent. You can have long-stroke such as found in the Garand and AK, short stroke as in the SKS, cutoff and expansion as in the M14, and even a "gas trap-like" system. Each of these concepts has its own subset of pros and cons.
The gas driver is just one part of an integrated system. As with most in life, it's a matter of compromise.
The direct impingement shines in longer-barrel (16" and up) applications where accuracy, particularly at longer ranges, is the goal. The simplicity, light weight and low cost for the standard parts of the direct impingement system make it the choice for most non-full-auto applications.
Direct impingement pros:
Direct impingement cons:
The gas piston system shines in short-barrel, e.g., under 16", applications, which require NFA Registration (where state-legal) for us civilians. The high port pressures found in short barrels quickly erode the gas port. A well-designed piston system can accommodate the changes in port size over time. For much the same reason, gas piston designs can be more tolerant of suppressors (ditto with regard to NFA and state laws). The advantages may increase where full-auto (ditto again) is concerned.
Gas piston pros:
Gas piston cons:
If you don't fire 1,000 rounds in a session, particularly if it's not full-auto, and you have a civilian-legal barrel length, you will be better off buying ammo and becoming more proficient than spending the money on a gas piston conversion. I'll submit that this will be the case for 99% of civilian shooters.
Now, let's go shooting!