I've used Zoom for one return trip to the UK (and MyTravel for 2, BA and AC for one each.) Zoom rescheduled our outbound to 3 hours earlierand via YHZ, 2 days prior. We turned up at check in and they said they couldn't contact all pax, so it was back to the original time but still via YHZ. They gave us a $20 meal voucher due to the "late" departure and the flights were fine.
My MIL has used them 5 times now in the last 2 years always without hitch or complaint and has 2 more trips booked already. (Yes she's here a lot and I work lots of overtime!)
An airline with only 4 aircraft is always going to be suseptible to delays a rescheduling due to equipment issues.
As a rule, you get what you pay for, but I can't find fault with their service and value.