There is benefits and drawbacks to every usability testing tool. People like usertesting.com because they can "set it and forget it" meaning they recruit all of the participants for you and offer automated unmoderated tests, then send you the results. It's an easy way to get a lot of feedback quickly.

While this may seem like a great way to save time and money, how does it really get you closer to achieving your goals of better understanding your users? Do you think that a test conducted in this manner is really attaining high quality results and valid data?

Empathy cannot be outsourced. It requires time and effort to get to know people at an intimate level. If you have stakeholders demanding usability testing with 100 participants and you're considering using a tool like this to save time, first consider educating your stakeholders on why it is unnecessary to conduct usability testing with that many participants. Five in-person test sessions will cost a heck of a lot less, take even less time, and result in very high quality and valuable feedback you can implement immediately. Plus it will help you and your team better internalize the flaws of your design and the needs of your users.

If you have more questions about these tools, usability testing, or other research methods, please feel free to call me on Clarity.