I did that switch. Used ProSeries in my small practice for 3-4 years, ran in parallel with UT for another two years (new clients went onto UT, but I continued my priors on ProSeries), then finally migrated all to UT.
Since I haven't used ProSeries for several years I can't speak to what has changed since then. I like UT diagnostics much better, and UT supports more forms including state forms (ProSeries didn't even support Form 8275, and it's a non-calculating form!). As a small firm I use PPR (pay per return) licensing and actually UT was about the same as PS on that basis, but with UT you are only billed semi-monthly during tax season instead of immediate payment for each return authorized. With UT you can send organizers for free. I like the integrated documents such as engagement letter, 7216 consent, which can be esigned.
There is a learning curve for any software, but I feel more productive with UT, less time spent figuring out where to enter something, or where a number on a form came from. Especially for entity returns.
I could go on but I'm sure others have comments so I'll stop here.