I own a Super UFO Pro 7 (34M), and not a UFO 6, but basically I guess it's only good for games up to 16 Megs + BB or for realtime save (if it is supported). Why don't you try renting various SNES games like StarFox, SFII, Killer Instinct, Pilotwings, Super Mario Kart, and see for yourself?
http://www.cd64.com had a page about the UFO 8; maybe that can help you if it's still up.