The Neo CD toploader is a brilliant piece of kit, I'm quite a fan
If you're not that bothered about missing out on the newer releases then the CD unit is a great choice to replace the AES.
Loading times can be a pain, but the software is cheap (by and large cheaper than the mvs counterparts), easy to find and many CD games have arranged soundtracks and bonus features that neither the MVS nor AES carts have.
You'll be able to get all the KoF's up to and including KoF '99; Last Blade 1 & 2; Pulstar; Ninja Masters; Neo Turfmasters; Neo Driftout; Overtop; Breakers and lots more of the really popular back catalogue stuff.
Plus CD only games like Zintrick and Ironclad.
Metal Slug 1 & 2 are available on CD - X,3 & 4 are not.
There are very few pre KoF '99 games that aren't available, but those that spring to mind are Fuun STB, Ultimate 11, Blazing Star and Waku Waku 7.
You can get all the Fatal Fury's (ex. Garou), AoF's and World Heroes too
If you want to do Neo on a budget then CD is the way to go
See Bluevodoo about get a set up and games
