I bought one recently and have been doing some sessions on it. Like you, too little time for riding properly and I had a couple of events coming up in late summer I just hadn’t put enough work in for.
Four weeks of fairly structured sessions of 40-60 mins 2 or 3 times a week on top of my regular one / two if I’m lucky rides a week, and the benefits were actually pretty good. The events went as well, if not better than prior years when I’d trained up for the events just by riding more.
I used these off t’interweb.
http://www.bikeradar.com/fitness/article/fitness-basics-turbo-training-24170/
You also need a HRM to know if you’re pushing hard enough (i was surprised by how easy some zones feel, conversely some are horrific)
I got a Minoura VFS-G from Merlin, about £120 with their online discount. So far so good, although the flywheel did come loose (easy enough to undo the cover and tighten the nut)
http://www.merlincycles.com/bike-shop/training/trainers/minoura-trainers/minoura-vfs-g-remote-fluid-trainer.html
[edit – and banging tunes and a stopwatch. And a towel, and a fan. And don’t forget you need a trainer tyre too]