I too enjoy the many uses of the Ryobi One+ system, and have several of the tools. However, I did pass over the trim router as my first foray into the routing world. I would have loved to have a cordless router to do the projects I was looking at, but I decided that I wanted a dedicated router, with a corded power supply, in order to do the things I wanted to do. I can't speak for the trimmer itself, but I find myself wanting for power some times with the battery with the cordless saw, so I didn't think that the trimmer would do what I wanted.
It may work for you well. But do know that I'm pretty sure the $50 price is what it's been for at least a year, if not since it was introduced. You could always come back to that if you need to down the road. Hopefully the system isn't going anywhere for awhile.