Original attraction to the software was the ability to connect with Outlook, and have custom tie-ins with our in-house built CRM to port over the data. They worked super hard to properly map and port our existing data. Pretty much nailed the quote as far as time and expense if I remember correctly.
Cost effective: we will save quite a bit over 5 years by hosting on-site, as we already had the internal infrastructure to host. Might not work if you don't have the infrastructure or staff.
They have been mostly excellent in regards to response for issues and working with us to resolve those.
OnContact does include everything with the price, so there's none of the nickel-and-diming you get with most SaaS software (just $5 more per month to unlock X feature!). I hate that with a fiery passion, so that's probably the top of the list on what sold me. Super above board in that respect. Bravo team.
Phone app is useless. It's not actually an app, just a webpage port. None of our staff can or will use it.
Outlook connection isn't great, but I think that's more on Microsoft than OnContact. We switched to G-Suite several months ago and support for that is minimal, so waiting to see further development on this. Again, any upgrades and new features are still included in the price, so definitely worth considering for that reason (yes, a plus in the negative section).
Interface is just OK, lots of clicks to do basic stuff. Lots of slide out drawers, which is OK on desktop but not usable on mobile. Lots of customizable search options and features, but it's too programmy in the language and execution, which makes it difficult for folks who aren't computer savvy to understand. Just no finesse in that regard.