I had a quickly assembled and temporary combo in a restricted space and it was a bit of a pain- I was always banging in to the thing. It was also quickly setup and the router was a bit heavy for the base, so was a bit tippy. That can be easily resolved. I sold this saw.
I am about to make another. I figure that I need the extension on the table saw so it may as well have a dual purpose. I need to rearrange a few things to give it the space it needs. It will have a proper base etc this time.
The only downside that I can see is the fact that you may have to move any table saw settings to use the router part. With limitless space and budget, everybody would have separate everything. In the real world, this is not a bad combination. The upside is predominantly space saving.