[J_Westy]

That Garbaruk needs an HG driver, which puts it in the same class as the NX and SunRace cassette..

Sorry, if I wasn't clear, but that's why I linked it -- "Standard Shimano" but works well on Sram... at least according to them.

 

[J_Westy]

First thing the mechanic does is he puts a gauge on the chain and says, “chain is pretty worn”. I say, ok, put a new chain on it. He says, no I won’t be able to adjust it.

I really should start wrenching on my bike. I have mechanical skills, it’s just I don’t have bike tools…

But it’s worth buying a chain and giving it a try. My rear cassette is a 12 speedSRAM NX. It’s cheap and heavy. It’s not aluminum and it’s only six months old. It doesn’t visibly look worn, so I’ll give the new chain a try.

Can't say if the LBS is trying to up-sell you or not, but for sure get yourself a ruler or chain checker, chain breaker, and derailleur hanger alignment tool and take care of this yourself -- youtube is your friend -- the park tool videos are a great tutor.

Cassette teeth are so contoured these days, it's not so obvious when they're worn out by just looking. I just ride it until the chain slips (rolls up the teeth) or it's crazy noisy after installing a new chain.

With NX, you have to use an "HG" cassette as opposed to an "XD" cassette, so you can't upgrade to GX without changing the driver on your hub, but SunRace makes some lighter options.

If you want to go even lighter, I noticed the Garbaruk HG 12-speed cassette says it works with both SRAM and Shimano drivetrains...

Garbaruk 12-Speed MTB Cassette – Shimano HG Freehub

Lightweight 12-speed MTB cassette by Garbaruk, compatible with Shimano HG freehub. Maximum performance and precision shifting. Made in Poland.

garbaruk.com