I've been using MON regularly on the AGP-MAN run for a couple of years now and they remain my carrier of choice.
Only irritations are the frequent flyer scheme that seems to be poorly administered and check in at Manch' where you have to get past the 'cabin bag police'. That's probably more the Manch' jobsworth mentality rather than anything to do with Monarch.
Only had one significant delay in two years and we were well informed and given scoff vouchers right away.