We bought an AceKard about a year ago and had no problems. When we upgraded the firmware on the DSi the AceKard started locking up randomly. We loaded the latest AKaio and the lockups were less frequent, but still there.
I just got the one from 5th Dimension and in the order I specified what version the DSi is. They preloaded accordingly and this one has not locked up in the several weeks we've had it. Ordering was painless and they kept us informed each step of the way. I sent an email to confirm the AK would be right for our version firmware and had a reply in minutes from them.
Under $20 and no shipping charge... I don't think the price can possibly be beat. And of course, the service on top of that.