To be clear, I am not representing 10X Management in these comments, except as a satisfied client (I have been with 10X since 2013).
10X has a portal for clients (like me) to maintain our profiles. We have a Slack and a mailing list. Most of my contact with them is through my agent, who will tell me about projects that I might have an interest in.
Toptal is more like a traditional outsourcing agency, 10X is modeled on talent agencies.
I have not worked for Toptal, I know some people who do. Anecdotally Toptal charges their customers approximately double the rate they pay their freelancers, though that varies. I understand their freelancers are under NDA not to reveal what Toptal pays them. I have heard a few complaints from freelancers that Toptal pays low rates and varies what they pay by geography. To be fair I have also talked to freelancers who are very happy working through Toptal.
10X Management takes a percentage of gross billings and pays the rest to me. I don't want to get into numbers but I can say 10X takes a lot less than 50%. They aren't charging customers double what they pay me, in other words. You can Google for comments on the 10X percentage, it's consistent with what agents get in the entertainment and music industries. As I mentioned 10X has consistently negotiated higher rates than I was getting on my own, even with their percentage. As a solo freelancer without much presence or PR/marketing the credibility and marketing and professional agents are worth something to me. The 10X founders are frequently on Bloomberg News, for example. Just not having to deal with invoices and collecting payment is worth something to me -- as a freelancer you want to make most of your work time billable.