The trouble with forums/support sections is you tend not to see the silent majority just plugging along. Fanboys, those with troubles, wafflers, those trying really exotic things, and the occasional shill tending to take up the majority of the discourse, though increasing internet has seen some that might not quite reach the level of waffler say a few things.
In general the simpler you can make life for an embedded device writing to an external file system the better off you will be. We might be reaching a tipping point where baseline options afforded by chips and libraries are stable enough in some things (if the SD cards themselves often feature ARM processors at or more powerful than the GBA it is running on then phones and the like...) that you can expect to push things but knowing the end results and knowing the chips that go into things... it will be a while yet before I don't expect to hold a device's hand.
To that end unless you have a reason to go for exfat (this typically being that you have a ridiculously large card packed with thousands of ROMS as you are unlikely to need 4+ gig files if you are just doing GBA stuff where almost nobody would ever have seen a file greater than 32 megs and even then 256 megs would have been it) then I would probably look more at FAT32. If you can further get into the habit of playing nicely as well then even better.
The EZTeam sent me mine and while I pushed it as part of testing my day to day with it is usually more in line with how I normally do things. Having an entire ROM set onboard (or even just English + Japanese of note that are not represented in the English stuff + any European stuff in addition to that) just seems counterproductive -- pick the games you like and that have something interesting to consider (in my case my general game collecting is about games I like, firsts to explore a feature and notable evolutions or implementations thereof). Most people of most tastes will probably get several thousand hours of that of just new play and if you like facing off against AI then... there is a reason I am still playing the GBA to this day (it was also far enough along in history that games had by and large moved from "levels 1 to 8 in a row" to having some measure of replayability or even constant novelty by default). Likewise I tend to roll with electrically stock, reasonably maintained, official devices and it is the custom screens, chips, clone devices, batteries, beat up old devices (the GBA is now the better part of 2 decades old) and the like where things start getting a bit iffy.
I have plenty of other GBA devices that do just fine (as was mentioned from the earliest everdrive discussions, if not way before that, the GBA was not a hard system for the flash cart/mod chip/emulator set compared to what came before --
http://gbatemp.net/threads/buying-a-gba-flash-cart-in-2013.341203/page-18#post-4756995 is/was nothing new as much as a collection of info already known and generally long since sorted but not necessarily written down in one place) so I don't necessarily know that I would have made a leap.
Were I coming in cold and looking to have something to ride out into the sunset on by splashing more than the bare minimum it would be a prime choice, with the EZ4 being the main contender vs the everdrive purely on a cost basis.
