The saxophone is supposed to be one of the easier ones to get a musical result out of. It is also fairly physical.

Polyphonic instruments posing a problem with ADHD is not an absolute rule, but I've seen more than a few people, especially at younger age, benefit immensely from a change from piano or guitar to the saxophone specifically.

The reasons could be many. Less reading while still struggling with technicalities, more deterministic fingering, less going on are just a few.