I had a Utopia on my prior Interstate. It was installed by the prior owner. I loved the back rest, but it did make the seat pretty difficult to re-install. The mount interfered with the plastic tab near the center of the seat fitting into it's recess. I don't know if this is common, or a result of a not quite perfect installation. Not a big deal, but something to be aware of.
Just follow the installation instructions carefully. I installed mine, not problem. On the hard to install the seat issue, those instructions probably weren't followed very well. Don't be afraid to make that cut, just try not to over do it, you'll be alright.