I have purchased a 2100 the other day and it came with Firmware 2.1.06. The 2100 has been working since then without problems, therefore it must be a production release and stable enough to hit the stores.
I did not install the update but I extracted it and had a quick look at what has changed (using a recursive diff between 2.1.05 and 2.1.06). Looks like there are tons of minor things updated in the php code plus some of the scripts, but nothing important really. The only changes worth mentioning are language pack capability for modules plus command lsscsi. All in all a rather disappointing update. I dont think they fixed the ftp auth bug either, somebody please check.
PS: in case there is some interest; I have simple instructions on how to unpack the firmware upgrade for inspection on Ubuntu (or any other Linux distro)