There are four, 5 now models of EZ4
The original 4
The original white thing with a miniSD, 256Mbit of NOR and 128 of PSRAM.
The EZ4 lite. Barely bigger than a DS lite slot and comes with microSD. Same specs as the EZ4.
The EZ4 lite compact. Very little space for GBA games and was aimed at those wanting a cheap DS flash cart. Same size as DS lite dust cover.
The EZ4 lite deluxe. The one with 384Mbit of NOR and 256Mbit of PSRAM. Same size as DS lite dust cover.
Modern ones.
The original EZ4 got a new batch a while back. Mainly removes DS mode. GBA sized and still 256Mbit NOR and 128 PSRAM and with miniSD again.
The current one which is a new case, black for the most part, microSD, still no DS mode and such.
All were upgraded to support SDHC and autopatching if you want to run the newer kernels on them.
As a DS card the whole EZ4 range is pretty pointless these days. I still use mine and it has a nice DS ROM and save dumper that saves me faffing with wifi or swapping a 3 in 1 around. To that end the EZ4 lite compact is pretty pointless, however all the other EZ4, including the straight up EZ4 lite, should be able to take SDHC and autopatch games if that is your desire, or if you want to stick with the older kernels it will still run damn near everything
http://gbatemp.net/threads/buying-a-gba-flash-cart-in-2013.341203/page-18#post-4756995 just need PC side patching and won't do SDHC.
That said if you do find a straight EZ4 lite these days you will probably have to replace the battery in it -- non rechargeable almost watch battery sized things were used and they have not been made in many years so will have likely gone by now.