It's fine. They are low frills, but perfectly fine. Be aware on most of their flights from IAD, the "business class" is just a slightly wider seat and an empty middle seat. No seatback entertainment, and no meal service. But you're also not flying for more than 4-5 hours.
A lot of their flights leave around 2am when a bunch of flights to that region depart. Beware Dulles is super quiet then = nothing is open, including airport lounges. Bring a book and a snack.
Just be happy you're not on the newly-announced Boliviana flight from Dulles:
https://onemileatatime.com/news/boliviana-de-aviacion-miserable-flight/