Unlike some other import carts, the cart connector has the extra space for games that need the extra pins on the sides and there is enough space and also provides enough space to fit either a SFC or SNES cart.
As far as compatibility goes, i haven't found a game that won't work, though I only tried japanese and american games, perhaps PAL carts will have issues.
Here's what it looks with a US cart and a japanese cart (Sorry for the glare).