If you want to do "hobby" stuff with our cameras then you could get away with the cheaper models. Even a home made model. There are plans out there that you can make your own using stuff found at any hardware store.
Heck you don't even need a rotator to make pano. You can do it standing up with your camera or on a monopod.
If you plan on doing this for money of on a more serious level then you should get the Agnos rotator.
It is like any tool. A serous craftsman will have quality tools as he relies on these to create his product. Joe Blow can get by with stuff from Wal-mart.
It is a matter of picking your tools. You get what you pay for.
I use the Anos Mrotator TCP short and it is a very good product that I trust to get the job done on every shoot. I make a living doing panoramic photography. Therefor I have to have a tool that will perform.