Chain checker. It's worth at least the couple of dollars in piece of mind. I've had chains in nasty gritty conditions be absolute completely worn out junk in 500 miles. I've had others last more than 3000 that only got changed because of upgraditis.
As noted, so much depends on how you ride, the conditions you ride in, & maintenance efforts that it's impossible to give a recommendation. Kudos for going to the bike shop to check & confirm. If you do need a cassette, chain, etc...You need not be confined to the ever-popular Sram-mano; There's lots of other manufacturers that make perfectly acceptable parts. Sunrace & KMC immediatley comes to mind.
--One good measurement is better than a thousand good guesses.-- So said some famous person.
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I shouldn't have to "make myself more visible;" Drivers should just stop running people over.
Car dependency is a tax.