For comparison I have got a Retrode, which is able to play SNES and Mega Drive cartridges on PC in stock form, and features 4 controller inputs (2x SNES, 2x MD). Along with plug-in adaptors that I bought separately, it can also be used with GameBoy, Master System and N64 cartridges (the latter one came even with two N64 controller inputs). Unfortunately no NES/Famicom carts supported so far.

That thing acts like a USB reader for the cartridges, is able to retrieve and write SRAM data back to the cartridge (take THAT, Retron 5). Of course it doesn't work with any specialised add-ons, since it is just used to dump the ROM and SRAM data on-the-fly. Other than that, game compatibility is just dependant on the emulator you choose to play with on your PC.
Firmware updates for the Retrode have been coming frequently.
A fine device for me to let me cheat through R-Type III with save states (the only way that made this damn tough game enjoyable for a wimp like me), and letting me back-up and rewrite my SRAM save data from various time consuming RPGs.
At the time speaking, the further development of the Retrode is on hold, but as the device is now, it works fine. Support for NES through plug-in adaptors would be nice, though. It is possible to hook up HuCards to the Retrode's SNES cart slot if you are able to build an adaptor on your own with the help of
these schematics.
I'd say the Retron 5 is a machine built upon Retrode, that let's you conveniently output directly to the TV and has all that emulation stuff hidden under a neat looking GUI. But I don't like all the restrictions that come with this machine.
Just for convenience, here's GameSack's Retron5 review which was already posted in the dedicated GameSack thread: