There was an iPAQ 3820? The 3830/3835, 3850, and 3870/3875 models I know, but 20? Perhaps a model distributed in a European or Asian market? Anyway, none of the 38xx series were SD I/0 capable, so such a card would not work; an important consideration for readers who may still use these models.
The size is small... it would appear to be exactly the same as the Spectec SD 802.11b card it seems, if not slightly longer. Mine measures 38.34mm end to end, compared to a standard SD memory card length of 32.00mm. A difference of 6.34mm. You say that it "extends only 5mm from the top of the device." This number is confusing. Does this number refer to the Dell Axim X5x type device in your picture? Since different devices have variable projection/depth for the SD slot, an absolute measurement of the card makes better sense.
"Todays devices have 802.11b built-in and you might want to take advantage of the faster speeds afforded by 802.11g." Did you compare throughput, upload and download speeds, with an 802.11b card on the same Pocket PC? My guess is not. If you had, you would have found no difference, as there is a hard ceiling on com throughput in all PPCs, at least up to WM2003SE devices. This limit is approximately 270kbps in my own tests and all tests I've read. Hardware throughput is often much faster, for example transferring from a memory card to RAM (your Axim should have no trouble playing a 700kbps video from SD for instance), but via a com port the speed limit is very low. There should be zero effective advantage in using a 'g' card over a 'b' card. The only real advantage is in connecting to Access Points which have been configured to disallow 802.11b device connections.
Guess I'm bored this morning and taking it out on you... sorry. Nice review, generally.