Red Branch BJJ - thoughts?

I haven't trained there, or know any of the guys there. But I think I've heard of them. Possibly on Reddit. I realise that's not a lot of help. From looking at it, it appears to be a sort of 10th Planet Hotbox, rather than a proper gym (hotbox are unofficial training groups, technically recently disbanded). Based in Crossfit Ronin? The page/IG suggests classes are run by some local blue belts (maybe a purple or 2). Under guidance of Jeremy Fields, a 10th Planet Black belt under Eddie Bravo based in California.

As for ability of the guys there, and the standard of class. I can't comment. But I would add that 10thPlanet HQ puts of extensive technique and instructional video regular. Take these videos, drill them techniques in clad, and roll with the guys there and you will get better.

What exactly are you looking for? Jiu Jitsu, or 10th Planet Jiu Jitsu specifically? What made you pick the above

A hotbox is like an unofficial 10th Planet gym. Usually run by guys interested in the system were there is no official 10th P affiliate nearby. They get together to train and are sponsored by an official affiliate. They get ranked by their sponsor and spread the 10thP system.
All hotboxs were recently disbanded. They are free to continue training in the 10thP system, but they aren't going to be listed on the website anymore.

I'm not in Dublin, so I can't help you with whats nearby. But the best thing you can do is probably go along and try a class

I have attended a few classes in RedBranch as a complete beginner and found the classes excellent.

The atmosphere in the class is relaxed and the instruction is of a good standard.

The format is drilled techniques for the first hour following by positional rolling followed by free rolling (generally limited to those with a few classes under their belt)

Can't comment on the affiliation discussion above as I don't know.