Recent transfer from Midgard here! I've been on Balmung for about a month now, and all I can say is that I wish I had moved earlier. I'm not sure what the economy is like on Siren, but things are actually cheaper on Balmung than they were on Midgard, aside from possibly stuff like... housing, which is in extremely limited supply here. I have found the server, overall, to be extremely friendly, and I'd say that unless something is tying you down to your current server to make the leap!

Good luck!