The Action Replay Cart can act as a save backup, not a direct save cart. But, the AR's other functions greatly put it over the top when compared to other carts.
I bought the one in the photo a couple of weeks ago and I have had no problems at all. Just plonked the cart in and everything was fine.
You can use it as a cheat cart, memory backup and import player and mine has worked 100% in all situations. Maybe it will fail in a year or something but I can't really see why unless I keep removing and fiddling with the cart.
EDIT - it also has the 1mb/4mb ram cart built in for games that need it but I haven't tested that yet.
I've been using it since I got my Saturn back in '08 and it's worked great.
I will say that once, and only once, when I booted it up my save files were gone but I shut off the system, took it out and put it back in and then it was fine. I think it might not have been in all the way.
Imports run great and I've played a lot of Samurai Shodown IV with it and it runs perfectly so the extra RAM feature works well too. Also Panzer Dragoon Saga will not boot up with this in the system; though I've read there's a code you can input to bypass that, but I haven't tested it.
Systems Owned: NES (1), NES (Top Loader), SNES, N64 x 2, GC, Wii; Master System I, Genesis Model 2, Sega CD Model 2, Sega 32X, Sega Saturn, Sega Dreamcast (US), Sega Dreamcast (JP); PS1, PS2, PS3; XBox; Neo Geo, Neo Geo CDZ; Game Boy (orig. Gray), GBA, GBA SP, DSi, 3DS; PSP (1000), PSP Go; NGPC.
I bought this exact cart from play-asia for christmas and I haven't had any problems with it at all. It auto switches between the 1 and 4 meg ram without a problem, and it hasn't failed so far. It also allows you to play games from different regions without any boot disks, and has built in codes.
Systems: Famicom with Nes adapter, Turbo Grafx, JVC x' Eye, Super Famicom with SNES adapter, 32x, Virtual Boy, Saturn, Nintendo 64, Dreamcast, X-Box, PS1/PS2 (slim), Gamecube with game boy player, Wii, PS3 80 gig
Handhelds: Neo-Geo pocket color, PSP, Game boy Advance SP, Game Gear, Tec Toy (Mega drive portable) Playpal (Master system/game gear)
Got: Atari 2600, Atari 7800Pro, Commodore 64, Odyssey 2, Sega Master System, NES, Genesis Models 1-3, Nomad, Game Gear, Sega CD Model 1, Sega 32x, SuperNES, GameBoys, GameBoy Pocket, GBC, Sega Saturn Model 2, GBA, Nintendo 64, Playstation, Sega Dreamcast, Playstation 2 Slim, Nintendo DS Lite, Xbox 360, Gamecube, PS3 Slim