It’s legit. It’s got many uses, but it’s mostly used to direct download Torrents, they keep the torrent files on their servers so others can direct download. You can also use it to download from many hosting sites as if you had premium on them, so no more throttling or download limits.
I’ve had been using realDebrid until the french gov. axed them. Last I checked it seems to still be viable for Kodi streaming. Premiumize.me works just as good as an alternative for direct downloads from hosting sites at least