Hi, I'm the co-founder of Formation and we won't have many reviews online - good or bad.
We have worked with over 1000 engineers so we're definitely not fly-by-night but we're relatively small.
We don't ask anyone to write reviews. We used to say something super neutral on our exit surveys about suggesting people write realistic reviews - good or bad - on Quora, but we removed that two years ago because very few people noticed.
The biggest factor is people we work with usually have current jobs and don't generally want the world to know they were doing focused interview prep the whole time - like there isn't really anything to gain by posting the review.
And very very few people have such a bad experience that they would want to write negative take-down reviews out there and for the people that have had the worst experiences we feel terrible about it and try to deep dive and see eye-to-eye before they depart.
So I think the combination of all of this is why there are so few reviews in general.
I would 1. try to talk to people who did it/are doing it and trust our team to try to connect you to people with similar backgrounds to you that aren't 'plants'. 2. trust our team in general. We maintain our generally positive reputation because we try to let in people for whom it works.
It's costly but the goal is for the outcome and negotiation to pay for that many times over.
But more simply, what we offer is expensive to run and I haven't had a pay check ever at Formation. You get mock interviews that would cost $150 to $500 each on a la carte interview sites. You get a dedicated team of 3-4 non-technical team members to help you day to day. We have a platform built entirely in house for managing your job hunt and interview prep that has numerous innovative features developed from scratch.