This is potential huge. I hope it works more seamlessly than the Element/IRC bridge, which is a hot pile of garbage and almost got me kicked off an IRC channel due to the formatting issues that the Element bridge introduces.
Best of luck to them!
While bridging to IRC does make you a guest, the amount of hand-wringing IRC people do about differences in formatting always felt disproportionate to me, especially in that IRC doesn't actually have an officially sanctioned experience. It's fine to DM a password to a Nickserv and set esoteric channel modes, but apparently looking bad to irssi/erc/BitchX/WeeChat users is a big no.
The long message -> file behavior is a bit silly and understandably annoying, especially in a help channel, but the amount of complaints I've seen of people not following <my-IRC-client-of-choice>'s highlight pattern is just silly. People get uppity because you appended the IRC network's friendly name in parens to their actual name? Oh no!
If a matrix user tries to write something too long for matrix+bridge to handle it will instead just paste a link to a website that shows the users text. Only the link to this web text clip will be sent to IRC.
If a matrix user responds to someone their matrix client + bridge will inline copy the previous lines and send it to IRC with their response.
Basically, the matrix bridge is extremely spammy even with normal behaviors. The sane thing would be to just break up the message into to parts and send it. The sane thing would be to assume anyone looking at IRC already knows what comment they are responding to and there's no reason to re-post it inline.
There are more annoyances but those are what come immediately to mind.
Yeah honestly I prefer the "automatic pastebin" behaviour, because the alternative is that walls of pasted text end up destroying channels. The Matrix bridge is mostly just doing what we ask regular IRC users to do; viz., use a pastebin for large content.
I've used the Matrix bridge to IRC a lot, and no one has complained. Of course, one has to remember to never use edit messages, or use the reply feature.
Ideally, these functions should not be available when connected to an IRC channel.