Pros
Billtrust does a very good job of bringing in people who just want to work. The count of self-important, arrogant jerkfaces is definitely low. The overall culture is supportive, trusting, respectful, and positive. Managers (at least the ones I've interacted with) seem to genuinely care about the career path of their employees, and actively assist them in attaining their goals. They recently switched to a work-from-anywhere model (which I think is a very smart move), and are working out the support structure for in-person interactions, which include WeWork, company events, etc. Work/life balance is taken more seriously here than in other orgs I've worked in. Culture, combined with other processes (see remote-first comment above) contribute to a good balance between work and life. I've had my manager not-so-subtly suggest I take PTO when it's been a while.
Cons
As with any job at any company, there will be frustrations, misunderstandings, and days where you just want to pull your hair out. I'm not going to conflate those temporary frustrations with systemic issues. As far as actual cons go, the only one I can speak to is that compensation for in-demand roles isn't market competitive is some areas. It's not so bad that people are leaving like someone just pulled the fire alarm, but it's enough that it opens up the door for possible poaching/recruitment, which obviously increases stresses on the team and the org.