Given that my state requires muzzle devices to be pinned and welded, I am thinking of installing an adjustable gas block. Is it worth going with an adjustable? My one concern is if something goes wrong with the gas block, I'd need to remove the muzzle device to change it which would be difficult when pinned and welded. May be good to keep it simple and avoid the additional failure point...

Simple is good, but if you really want an adjustable gas block, maybe a 2-piece design will work best for you.

A two piece gas block like mentioned could work; you'd be able to switch it out if it failed for whatever reason. If this is your only AR and you plan on getting a suppressor or tuning your gas to specific loads, an adjustable gas block would be a pretty good option, but if you're just building a standard-ish rifle with a regular, nitrided or otherwise treated 4150, to shoot 55gr to 77gr commercial loads, to blow through watermelons or paper, to protect your family, to ding steel, honestly, an adjustable gas block is unnecessary. If you're getting an expensive, stainless steel barrel with particular rifling, with a matching bolt, and you're going to math out a "perfect" load to shoot at half MOA, or if you're going to be doing 3-gun or similar, yeah, the adjustable gas block would mitigate some extra recoil once it's tuned, so it could be a good option there.

However, if I was to ever pin/weld a barrel, either to the legal limit or due to state law, I'd probably get a slim muzzle device. That way, you can change gas blocks if you need to(unless it's defective, you shouldn't have to replace a gas block period), or if you decide at a later date that you want an easy way to switch to suppressed fire without adding a ton of gas pressure. Faxon makes a slim muzzle brake as well as a slim flash hider. Both of them are really effective versions of their respective type of device. I know other companies make this kind of thing, but I was looking at Faxon barrels earlier and stumbled across these, so they're fresh in the mind. You might have some sort of hybrid compensator in mind that you want to buy, and there's no doubt that there are plenty of hybrid devices that are great all-around options, the EFAB comes to mind, but they're usually expensive.

I said that I'd probably get a slim muzzle device, but if I was actually in that situation, I'd consider taking a gas block off of one of my other ARs with decent round counts to ensure function, and getting something like an EFAB. It would be a tough choice though, and you aren't losing a whole lot by going with a brake over a hybrid comp. The biggest thing will be the flash. If you shoot at night, or if you expect some sort of "battle" scenario happening, that could be a deterrent.

Faxon offers a nice small diameter FH that allows you to slip a block over it off and on. Ck them out.

An adjustable gas key is also an option.

Nothing will fail by using a quality gas block. An adjustable with .556 is not needed for reliable function, all things considered.

A gas block is rarely an issue.

Decided to keep this simple and use a standard has block. Thanks all for the input!