I'd call it a small con, but I'm basing that on comparisons to anime cons I've attended, which tend to be pretty large scale events. I'm guessing since pony is a fairly specific fandom the cons will probably be smaller compared to something more general like anime or comics. I also get the impression the pony craze has died down considerably in the last couple of years, so I'm guessing it's smaller than if I'd gone in say 2012 or 2013. I don't know how the one I attended ranks against other brony cons though.
I would actually say the pony fans at the ponies-only convention were quite a bit less obnoxious than the pony fans I've encountered at anime cons. This might have something to do with the fandom dying down and people who were just on board for the fad moving on to other things, though. A couple of cons I went to when the pony thing was just getting started the fans would show up wearing pony costumes and shirts and spouting memes from the show, and just generally behaving like annoying squeeing teenagers. The behavior of the fans in public combined with all the pony-related autism happening on 4chan at the time was one of the things that put me off and made me steer clear of anything related to MLP for several years. Bronies were basically the Juggalos of the internet. Sadly now that I've gotten into it at the tail end of the fandom I regret not looking past this and at least giving the show a chance, but what are you going to do I suppose.