Good for automating repetitive tests (smoke&sanity tests). Good for automating processes that does not require too much configuration or dynamism.
We are happy with their quality of services and will definitely continue to use your tool.
Overall, I really like the service. I particularly love that is does not require an engineer to get something done.
Inability to link test suites so that when one ends, the next is kicked off. There is a workaround for this, but it requires multiple parallel user accounts.
Sometimes it was hard to get consistency in our Test Cases, some due to the product not being able to accurately identify an element and some due to our own complex DOM.
Reports could be clearer. Lack of full-page screenshot in some browsers but possible with custom function.