Hope you don't mind me asking but how would a decent spin bike (gym quality) compare?
I've used these a lot and even the better ones don't compare well with your own bike on a good Turbo trainer.
A Turbo will take you as close as static training can to a session out on the road. Your body is in the same position, the thing is set up for you (crank length, saddle height, saddle reach, stem, everything).
Even the feel and sound of gearchanges is somehow familiar and reassuring during a Turbo session...
Another benefit of the Turbo: They are super-doop for getting your set-up right.
Another caveat: If you don't have an old wheel with an old tyre on it, just hang onto an old tyre and pop it on your rear wheel if you're expecting a few weeks or months of Turbo-only. Turbo use does odd things to rear tyres. Don't feel the need to fall for the old
"You need a spare wheel with a fancy Turbo tyre on it" flannel. These people have a job and have to sell product, but you'll be fine with an old tyre on an old, knackered wheel.