It's an interesting keyboard. It's neatest feature is a built in calculator run off a small battery. The keyboard itself is infamous for being very unreliable, but you are lucky since yours is working. It uses a mix of different switch types, primarily White ALPS, with a few linear Yellow ALPS, and a Futaba lock switch for the calculator.
Build quality is the same as all Focus keyboards, mediocre, it won't fall apart on you but it won't survive a war. It's biggest perk are the double-shot keycaps that are quite beautiful. The only way to get new keycaps is to buy another keyboard that uses ALPS sliders, you can find a Focus FK-2001 quite easily and cheapily and steal its keycaps, which should be identical to the ones on the 5001.
There's also two sets of doubleshot keycaps for ALPS on mechanicalkeyboards.com, dolch and olivette.
For $55 it's not a bad deal for a relatively unique keyboard. You'll have a lot of fun with it if you've never tried ALPS before.