That depends on what your running for BGC and buffer weights and spring weights.
Lots of things aren't needed, doesn't mean they don't have a valid purpose.
I like the SLR blocks with the detent system. Most of the ones with a set screw just end up needing to be drilled out if you want to adjust them after a couple thousand rounds.
At this point I plan on running a True North Arms Tube Kit (likely just a basic run of the mil so I can save some money) and Colt Bolt Carrier Group. I figured if I got the adjustable I could at least adjust it to the least gas required. If you guys think its not worth it to start off then I won't bother.
As noted the SLR is excellent & superlative arms gas blocks are also good. Both have a good detent system for adjustment. RDSC carries both brands.
Older adjustable gas blocks with a set screw as opposted to a hex bolt did tend to become 'non adjustable' after a few thousands rounds. One trick to avoid this is to move the screw after a range trip, open & close it 4 or 5 clicks either direction from you preffered setting. That will keep the carbon deposits from freezing the set screw or adjustment bolt. Some adjustable gas blocks recommend this in their instructions.
Rdsc has them, fit perfect. Helped my buddy with his assembly and worked great