As this is rather long, I'll but the key points in bold.

Partner and I took Avelo Air (XP) twice, mainly because we like Burbank airport much better than LAX and they fly (a couple of times a week) to destinations we were going to.

The first time, EUG-BUR, the flight was uneventful. Very bare bones and you pay for everything like carry-on bags, but we were fine with that since they were the only EUG-BUR nonstop at the time.

Seven months later, due to the relatively good experience with XP, we took them again flying MFR-BUR, which was the inbound of a round trip - we took WN up from BUR to a different city.

On the morning of the 4:30pm departure, we got a text saying the aircraft has mechanical issues and it has been rescheduled to 9:50am the next morning. No alternate XP flights or interlining to another airline for the day of travel were made available. We were upset, but tolerated spending another night in Medford. The text said they will reimburse up to $150 of hotel expenses per reservation. Finding something non-Motel 6 quality for that price is hard these days and I'm guessing this is not nearly enough for reservations with many people and they need multiple rooms.

We booked a Hampton Inn for $175 with AAA rate. The next morning another text read the aircraft was still being repaired and the flight won't depart until after 5pm. At that point we decided we couldn't rely on this airline, felt certain we'd be stuck in Medford another night and booked a UA ticket connecting in SFO at twice the total cost of the original XP fare. We did get a full refund from XP. The XP flight did in fact finally depart that next day, albeit a couple of hours later than the re-rebooked time. We're putting in for a delayed flight compensation through AMEX Platinum to cover the hotel and extra airfare (it doesn't seem XP will reimburse $150 for the hotel since we ended up canceling with them).

A reddit post indicated another person was delayed for a day on our same booked day likely due to the same aircraft, except they were flying FCA-BUR. XP's schedule indicates that the same aircraft was due to fly BUR-FCA, FCA-BUR, BUR-MFR and MFR-BUR all in the same day.

The main problem is the aircrafts are stretched thin and as their network is limited, there are no alternative flights if an aircraft goes MX. WN has similar aircraft scheduling, but they generally can accomadate passengers due to multiple flights to multiple hubs from just about anywhere not to mention having a shot at getting replacement aircraft. If your XP aircraft goes MX, you're stuck in whatever city you're in unless you pay through the nose for last-minute fares with other carriers.

No matter how convenient Avelo seems on paper, we will not use it from now on. Flying with Avelo is just too risky for us.