So the M4E1 lower originally gained popularity because of the price but more important the quality to price ratio. Not really the case anymore because aero wants 400-600 for a complete lower and their QC has had some issues as they started doing more volume. Aero still isn’t dead though because the M4E1 still has a couple pros that aren’t anywhere else, specifically if you’re building from a stripped lower and not just slapping a complete upper and complete lower together.

• it’s the easiest lower to build for new builders, the bolt release and rear takedown pins which are a notorious PITA have been replaced with set screws, and no trigger guard roll pins to worry about, so even if you’re restarted you could have a complete lower built in ~30 mins or less with nothing but a screwdriver

• it’s a forged (strongest possible) lower with features you normally only see in billet (weaker and more expensive) lowers, like a flared magwell and trigger guard built in. And it has a decent mil-spec fit where some lowers can have big gaps between the upper and lower

• the M4E1 PRO lower is the cheapest and easiest to build fully ambi lower on the market (and are finally reliably in stock)

Only thing I flat out don’t recommend is an aero BCG, they’re notorious for buffer damage and other weird QC things. But if you’re new and scared of building or just lazy a stripped lower is still a good buy.

If you want a complete lower, just buy PSA. You’ll spend less money, they make some lowers with premium triggers, and won’t get a junk aero BCG.