I'm quite happy most of the time about it. Seeing result immediately is one of possible benefits, e.g. when changing language, color, ... . That being said I would welcome, some undo (revert, cancel) in some cases tho.

Long time not working with MIDI files. Aren't you mixing track and channels? Why would you play multiple track at once?

What about just made one, take some USB eqiuped chip PIC, SiLABS ... They are with up to 2MB of flash to use this days. With little FW you can get from around the web turn it into FLASH drive. You can even sell them to company a get some money back for trouble :)