It allows you perform real-time save-and-restore states on an actual SNES console. The SNES power adapter passes through it, so it retains your save state even when you power-off the SNES. Even better, you can load up some AA batteries and take it to a friend's house...then pick up where you left off. It also supports true slow-motion so the game runs at 50% speed. The features are activated using button combinations on the controller.
Select+R(shoulder) - Record State
Select+L(shoulder) - Load State
Start+L(shoulder) - Slow Motion
Start+R(shoulder) - Alternate Slow Motion (resolves flickering in some games)
Of course, you can cheat with save states, but it's also useful for games that have no save system or a ridiculous password system (Megaman X2, I'm looking at you!).
It's really cool how this device demonstrates that the SNES has an independent sound processor. Even with slow-mo enabled, the music and sound effects are normal. If you load a state, whichever music was already playing continues, uninterrupted (even if it's the wrong music for the scene). If you're cheating by saving and restoring during a boss battle, the battle music is never interrupted as you save and load repeatedly. I'd have to say, this is more slick than the way an emulator handles it!
It came with a list of games and codes and I assume the codes improve compatibility, but I've tried some of those games without entering any code and they do seem to work fine. I'll have to do some testing to know if it helps to eliminate the flickering that happens when slow-motion mode is activated.
I'm interested to find out what the codes do. Does it have something to do the game's memory map? (HIROM, LOROM, SRAM, ...) If one of you devs can see a correlation, maybe it will be possible to know the codes for newer games that aren't on the list.
I remember a kid in the neighborhood was impressed that I had collected all of the Banana Birds in Donkey Kong Country 3. He wanted my save file on his cartridge for some reason. It took several tries because it would lock up most times, but I was eventually able to get my save file on his cart. My technique was to create a state just before the game was about to write SRAM, then power off, switch carts, start a new game file and load the saved state.
I checked eBay just now and saw a non-Plus version. I didn't know that this one existed. Apparently doesn't have the power pass-thru and doesn't accept batteries. I guess that one is only good if you leave the SNES powered on.
Pictures of my documentation:
