UserTesting can be instructive in terms of understanding whether people understand your copy, CTAs, and intended flows but generally, I've found the quality of their panels to be pretty low. You're almost always getting people who are not your actual users, so the feedback can only be generally applied as above. I find whatever web analytics package or packages you're using are generally able to provide much better insights.
I also really do believe in *real* user panels. Buying pizza or offering small financial incentives to real users to click through new flows where they are talking out loud or answering specific questions is going to give far more actionable insights than anything else.
What I like to do is take my best guesses as to what's not working or what I'm looking to improve and then discover/validate via real in-person customer panels.
Happy to talk through this in more detail with you in a call.