Pros
The people on the individual teams are great. Depending on what group you work in, and what discipline, you will get active involvement in your career or absolutely nothing. There is a lot of opportunities in some groups to collaborate across lines of business ("segments") which is unique in comparison to most of my corporate roles in the past. Prior to the sale to Thoma Bravo, this would have easily been a 5-star review and genuinely a company I could have seen myself staying for as long as they would have me.
Cons
Even before the sale, there were some cons (disconnect between disciplines, not prioritizing technical debt, etc). That said, I think there are cons at every company. However, after the Thoma Bravo sale things have just gone downhill constantly. From the beginning they spoke constantly about buying Bottomline "for the culture" and then proceeded to strip the entire culture away within a year. There used to be just small things that Bottomline would do (e.g. early-close at 2p ET on days before a holiday or holiday weekend) that all together made you really feel like Bottomline cared about it's employees. Charity matching every year, a wonderful program where they would provide scholarships to young people, etc. Now, I think for most US based roles they fear for their job regardless of their position.