Purchased 2 Regular Monos Carry on and did 3 weeks in Europe over cobblestone streets. So far so good, they appear well built. Ours were delivered in August within 10 days.
Only issue for both, often had to correct direction as it swayed, even on flat airport flooring. Not sure why.

Reg Size Monos - AC was no issue, Easyjet no prob either but with budget airlines, you pay xtra fee for carry on - still super cheap.
If you buy the Pro or Plus size, it may become an issue one day but so far I never saw anyone forced to check carry on.
With newer planes varying, some bulkhead storage bins were smaller and configured to slide in flat/sideways. i.e. bins not deep or tall enough
AC pre-boarding announces free checking for those willing. Free for now...
AC Intl Basic Economy fares = $75 per direction for 1st checked bag (can add up quickly)