Just remember that not all kinds of files compress. This won't help with images, music and movies. If your storage card is full of text files, maybe this would be worth it.
Probably, but it sort of depends. If the programs have some kind of compressed data files, they wouldn't get compressed further. (I don't know for sure but I suspect some games would store their gfx in a compressed format.)
The best way to tell is to zip up the data you want to use this program on and see how much it compresses. I bet this thing won't compress as tight as zip (for speed considerations) but this will at least give you an idea of how small it will get.
If this is designed right it should be seamless to use, meaning all of the zipping and unzipping is done in the background which is the way I read that it works. However recovering zip files is much much harder if something goes wrong so you would need good backups. And can you use the zipped storage card with a card reader?
All File Type
SpeedZip can zip/unzip all type of file, such as Video, Music (MP3, and others), Image (all type), Word, Excel, Games, MultiMedia, Microsoft Reader, Programs and all of your files.