My family and I flew Avelo BNA-HVN-BNA over Labor Day weekend. It was our first time on the airline. Overall I was impressed. A few things I came away with:

-Arrivals at HVN were easy. We had a checked bag and two checked car seats. They were available within minutes of our deplaning. Rental car counter is right there at baggage claim; cars are just outside the arrivals exit door and to the left. I think we were in our car within 20 minutes of deplaning.
-If you're being picked up by someone at HVN, it seemed kind of messy. Not a lot of space for cars at arrivals.
-Both flights, 9/1 BNA-HVN and 9/4 HVN-BNA, were pretty full (but not completely).
-Avoid row 11 of the 737-700s if you can. This is the row before the emergency exit row, so the seats do not recline. Additionally, I can't prove it but I think this row has the least pitch/leg room of any row on the aircraft.
-We had two adults and two children, all on the same reservation. Did not buy seats and checked in around the 24 hour mark. We were split in groups of two (one adult, one kid). Two separate parts of the plane on the way there; Same row (middle and window on each side) on the way back.
-Leaving HVN, the aircraft was boarded through both the front and rear doors. I was impressed with that and thought it made boarding faster.
-Boarding at HVN takes place on the tarmac. I think it is kind of cool to be able to see the aicraft close up from the ground, so no complaints from me. Maybe a different story if the weather were bad.
-No water provided on either flight. No big deal; bring a bottle. Filing station is easy to find at HVN. The only filing station I know of at BNA is closer to the D terminal, just past security.
-No dedicated gate(s) in BNA, though we departed from one end of BNA's A terminal and arrived back at the other end of it.

Added later after re-reading the posts above: pics of terminal from 2021 are still a fairly accurate representation of things. Also, completely agree with the slamming on of the brakes at HVN arrival! Be ready. It was a fairly extreme stop. Also, there is TSA PreCheck at HVN now.