As far as I know, they only recently came to the forum and most of the forum users heard about them for the first time then. It is certainly still new to Bitcointalkers.
They paid 100 users to use and review their service. Did not a single one of these users continue to use the service afterwards? That's a pretty big red flag.
Aside from pricing which i find rather high (especially because i live on developing country), i got stuck few times (either due to bug or mistake on their guide) when i attempt to move my Bitcoin through few means. So i wouldn't be surprised if nobody continue to use the service.
Almost all reviews pointed to the complexity of using the Mixin service. At the same time, we are talking about the users of this forum, who are mostly familiar with Bitcoin transactions. Although it was not realistic for many testers from the forum that someone would use this service, nevertheless, they held more than $200 million