i have an m1 and can’t imagine another yoyo that would be more fast or stable or more fun to play.
aside from the obvious differences (response systems, shape and weight, and extras like hubstacks), and aside from preference, what makes other metals so much more expensive and desirable?
Hubstacks are the biggest difference…
Yep, if they made an 888 w/o hubstacks it would be about $100. And also some yoyos have a swirl or splash affect ano on them that make them cost more cause of mor manual labor such as CLYW and splash YYF. There are also B-grades that dont play as good cuz of ano defect or vibe but still have a cool ano effect so they still cost more such as a B-grade CLYW. Basicly ALL CLYW.
“Feel” is something that every yoyo has. No yoyo has the same “Feel”, so that’s what makes them different. “Feel” can come from many factors, such as size, weight, shape, and how well it was made. That’s just one of the things that make yoyoing awesome: Variety. If you feel that the M1 is the perfect yoyo for you, then that’s fine! “Why fix what ain’t broke?” 
trust me i’m not worried that i’m missing out on something. until i can try a more expensive yoyo without buying it i’ll trust my m1 is the best thing for me. but hubstacks do look like theyd be fun 