One of my favorite little upgrade for the AR15 is the Norgon Ambi-Catch.
This is a drop in replacement magazine catch that gives you the ability to release the magazine from the left side the of rifle. Certainly not necessary to have, but very nice to have.
I picked up another couple last week. I never noticed it was designed to be easily disassembled for cleaning if necessary.
It is very easy to take apart with a small punch, and goes back together very easily.
This is my absolute favorite left side magazine release, and I highly recommend it. It is easy to install, easy to use, durable and simple. I think it should be standard on the AR15 family of weapons.
I know the Canadian military uses them. I’ve seen documents claiming that the US Military is authorized to use the Norgon Ambi-Catch per the commanders discretion, but I haven’t heard of our troops actually fielding them.