After much pondering, I made the decision to learn the concertina. With the collection of strange musical instruments in my house, it was inevitable. I took a cue from my wife, however. When she decided to learn the banjo, she picked up an ultra-cheap model to see if it appealed to her, and upgraded a few months later. The logic was that if she wasn't going to stick with it, better to waste the least amount possible on an instrument that sat at the very bottom of the playable range. Sure enough, she stuck with it and upgraded a few months later to a much better instrument.
With that pattern established, I picked up the D40 from Musician's Friend. I've been noodling on it for about a week now, getting used to it. I know that I'll want to upgrade, but the D40 is certainly playable (although I wouldn't want anyone but myself to hear my playing right now) and I think it'll serve fine for learning the basics. If a six month lifespan is normal for the instrument, mine should be wearing out just in time to add a better instrument to my Christmas wish list.