Not a concertina player but have been to there melodeon weekend. I found it (and the general consensus seems to be) very good, with excellent tutors and a really friendly atmosphere. The work, however, really starts when you get back home afterwards. I'm sure you'll enjoy it, learn lots and meet many new concertina players.

There have been worries on Melodeon.Net about the late issuing of application forms and concertina players have been worried about the lack of materials. Apparently Dave Townshend has been very busy (he's the guy who runs it) but I'm sure you'll get them before the weekend.