My review on Scribophile is rather mixed. As a member for several years, I have enjoyed the opportunity to network with other amateur writers. In fact, networking is perhaps the greatest use of the site.
The critique system works best once you have established a cadre of reliable critiquers, otherwise, you will find yourself wasting time on sifting through critiques that often have little intrinsic value. In part it's because everybody has to learn how to write a critique (that's just part of life, inside or outside Scribophile) but also because some people take pride in having no clue what it is that they are doing.
However, once you assemble a reliable group of critiquers, you've found a pearl of great price.
The greatest downside, in my opinion, is the forums. They are moderated in a rather arbitrary manner, and both the mods and the owner can call out and shame members publicly. Even if you pay for the premium account (and paying for premium is really the only way to use the site if you write novels), your account can be closed at the owner's discretion. And his discretion has not always proved understandable over the years.
Despite rules against discussing politics and religion in the forums (and hey, once upon a time, the rules of etiquette dictated that politics, sex and religion were verboten in polite conversation for a reason, so I cannot complain), the forums have still become a toxic wasteland. New members get mocked for asking questions that seem "simple" or "common." I have seen members mocked for everything from mental illness to their chosen writing genre to their financial status. It can get brutal.
The effort taken to combat the toxicity of the forums is an arbitrary system of strikes and banning that is applied differently depending upon the person. The rules change based upon who is being reprimanded.
The TL; DR version essentially boils down to: stay out of the forums. Join small groups and get into the mix to network. If you write poetry, this site is probably not a good fit both for its format and for the attitude taken by many members towards poets. If you write novels, you will find that it's very impractical unless you buy the premium account.
It's also worth noting that many of the members who have achieved success leave the site. What this means is that it can be difficult to get mentoring or significant input from somebody who actually knows the ins and outs of writing. Most advice will be coming from amateurs. This isn't necessarily bad, but it's something to consider.
Give it a try using the free option for a few months and then make a decision for yourself.