This has become a really crowded space. UserTesting.com, Validately, Loop11, userzoom, userlytics, etc. As other commenters have alluded to, it really comes down to participant demographic granularity. If I can't specify my target audience very easily and you can't deliver them at the number of participants I need, then the best user testing tool in the world will be pretty useless. This is why usertesting.com can command a premium. I can get extremely granular with my screening criteria and start getting results within an hour.

Also, it's worth noting that it's much more difficult to do native app testing, especially on iOS. That's another competitive advantage the bigger players have that is much more difficult for newer entrants to match.

Fwiw, the best user testing insights I've been able to get come from live, in person contextual intercepts (e.g. at the bank after customers have just wrapped up their business with the teller..."Wanna give our new mobile banking app a spin and get a $20 Amazon card?") and online intercepts using ethnio for screening and lookback.io to handle recording the actual test sessions.