What do you like best?
User testing is very easy to use, and you can pick up assignments when you want to. If the application is open, it will alert you when new tests come through, so I'll often stay logged in when I'm working on my laptop and find that I'll pick up a test or two that way. There's also an app for your phone, so you can get tests that way as well.
What do you dislike?
You need to be in almost complete silence, which is understandable as it's a screen and voice recording, but can make it awkward if you have roommates, unexpected visitors, or forget to silence your phone. Unless you're logged on to the website fairly often, you won't pick up a lot of tests, as you will only qualify for a few out of the many that they offer.
Recommendations to others considering the product
It's a great way to get feedback from ordinary users rather than industry professionals, so you'll have a good sense of how your audience perceives the product, as well as any major issues that the app or website may have. It's also a great way to make a little extra money if you serve as a tester.
What business problems are you solving with the product? What benefits have you realized?
I use the program as a tester rather than a business that needs reviews, but one of the great things is that it is all just honest reviews from users, so you'll get a really good idea of how a new website or application is going to be perceived by people in the real world.