@OP~got my daughter a Trek 7.1 FX last year as her 1st adult sized bike w/ 700c wheels at age 15. No longer using MTB style. she loved it! much happier with that style and wheel size. got the same for son and wifey this year. you can find used ones on CL but be very careful sizing them. I made a mistake for wifey and now son got a new bike he didn't really need and I would up buying a 2nd bike just so that my original plan of getting one for wifey came true. anyway that Dick's Diamondback bike looks a lot like our Treks that we are very happy with. if they have your size and you test ride it - I'd say it was a safe bet. the brand has been around a while too I think, which is a plus. you might ask if you can return it if you have buyers remorse after a week of riding it, just in case. if you can find/afford the Trek it might be a better bet if that style is new for Diamond back. the Trek 7.* FX model has a lot of followers and probably for good reason. you might also check the valve style and see if you are comfortable with Presta. if the bike comes with Schrader, you might find that more convenient, as do I. the 7.3 I got for wifey has Presta and I'll be drilling & swapping which is a minor hassle, but still a task I'd rather have avoided.