Ok, I'll try to explain as best as I can.
This version is a port of the Open Pandora version, also by Dave18, which is based on
the latest an updated version of FBA for Windows. Theoretically, it supports the same games as this last one (more than 5500, including Megadrive and PC Engine); practically, only arcade games (about 2800 games) run - unless i'm doing something wrong with md and pce - and not all of them: some (for example, CPS3 and larger Neo Geo roms) don't run on Caanoo due to insufficient RAM (but they obviously do on Pandora). Games that work, however, run reasonably smooth (CPS1/2, Neo Geo, Cave, Toaplan) or pretty slow (Sega).
I didn't test Reesy's port (the download link is down: could someone please upload it to OpenHandhelds, if only for archival purposes?) but I do know it is based on the GP2X version beta 7.3 by HeadOverHeels, which supports roms (arcade only, about 920 games) from FBA for windows ver. 0.2.96.72 (dating back to 2007/2008), except for Neo Geo games, which are from ver. 0.2.96.85 (=MAME 0.125u6).
I was an enthusiast user of the GP2X/Wiz version and I remember that, out of the games supported in theory, only roughly 690 did work: forum member bman did a great job sorting them out and you can still find the results of his work
here. Compared to the Caanoo ports, this one is still the only version able to run the more RAM-hungry games, because it uses a caching system similar to the one implemented in the Neo Geo and CPS2 emus.
I don't know if Reesy's port had this feature too but, if it did, I would advise Dave have a look at it to see if he can implement it in his port.