I used the 300 regularly pre-pandemic...
my observations were around peak holiday times it was well used in general for the guest houses around Newington area and locals from Newington & Southside to Airport.
Between Chesser and Airport it was mainly Air Crews and workers I saw Airport bound, think mostly it was used by locals to South Gyle and Gyle Centre
It was also an extremely handy link from West Edinburgh to South Edinburgh (Southside, Newington, Cameron Toll) because it completely avoided all of Gorgie, Dalry, Haymarket, Princess Street and Bridges
(There were quite a few people like myself, that commute from West Edinburgh to Surgeon's Hall, Southside and Newington and whilst the early morning buses weren't rammed heading into city, they were surprisingly well used.
I'm not sure if things will ever return to pre-pandemic patterns, but I'd love for the 300 to return as before, but I'm not sure we are at that point now *shrugs*