This is really one of the best entry-level trackers. Also the staff are very kind as opposed to the often ban happy staff of other entry levels. A great tracker to be a member of whether you are just getting started or are long in the game.
The high-speed label means basically nothing in UNIT3D. All it means that one of the peers seeding the torrent is added as a “seedbox” on some users page. (/users/YOU/seedboxes).
Anyone can add any IP as a seedbox. On average these torrents may have better speeds but it means basically nothing in any concrete case. The “seedbox” peers are just too variable to rely on. The peer count is almost always going to give a more reliable indication of expected speed.
DCC is a Scene focused tracker. The Scene releases stuff in RAR files. The primary reason for this is that lots of content is on usenet which has file size restrictions, so files need to be split up.
So practically the RAR chunks are the original files for scene releases. If you want an exact copy of the release you need those original RAR files. This can also be relevant if you want to cross-seed to other scene focused trackers.
Bittorrent has no restrictive size limits like this (torrents actually don’t have a theoretical size limit, but clients will). So the RAR file is unnecessary and many trackers that have less of a scene focus will extract the files before creating the torrent. Also for common content like audio and video they are already compressed so the RAR is just adding (a tiny amount of) overhead.
It is basically personal preference. If you don’t like RAR DCC probably isn’t the best tracker for you. There are many others that post just the media files. DCC does tag torrents UNRAR to help you find what you are looking for but there is no way to filter to only UNRAR torrents on-site. However some search tools (like Jackett) will let you filter to UNRAR only.
My main go-to resource is https://www.reddit.com/r/TrackersInfo/wiki/official_recruitments.
They are pretty hard to get into. Not much official recruitment and invites are relatively hard for users to get. IMHO they aren’t really worth it for how hard it is to get in. The tracker is also a bit weird and I don’t personally find it is for the best. However they are home of HONE and one of the few places where you can find 1080p WEB-DL with modern codecs. So I would be lying if I said I didn’t use my account there.