I'd recommend trying out their respective demos. Ours can be found here:http://fxhome.com/products/demo
Ultra, I believe, is aimed specifically at chromakeying. I think it can also provide live chromakeying.
However, that's about it, as far as I'm aware, and it also has the rather high price tag that you mentioned.
CompositeLab, on the other hand, or even more so VisionLab, is designed as a general compositing toolkit and can do all kinds of things. It doesn't do live comping, but it does offer lots of opportunities for other shots that might not be possible in Ultra. And there's also the price difference, of course.
But, yes, I'd recommend trying out the demos of both and seeing which would best suit the nature of your online business.
Let us know if you have any questions!