Haven't used Flexjobs right now, as I just clicked on the payment button. However, I'm here because I really liked Flexjobs last time I used it, 2-3 years ago.
I had lots of interviews, all the people I interviewed with were very pleasant and knowledgeable, and all job suggestions were relevant to my skills.
Basically, all other job-searching sites I used so far, left me with a very bad impression, and FlexJobs was far above.
I'm glad to pay for such services!