I have both of those among my presses. The 6mm dies with the cheap green one work fine for 1/4" eyelets. The ones that came with mine arguably press better than my more expensive dies. I can't speak for longevity, but I have no complaints about the results. The main issue is that the base die is way too wide to use on sheaths, so you'd need to grind a good bit of steel off. The press and dies have a weird shank system as well, so the dies won't fit other common presses and the press won't take any dies not made for it.
My identical arbor press is kind of a piece of junk, but others have been fine with them, so I probably got a bad one. The hole in the ram is 1/2" I believe and pretty much there specifically for the three fittings that come with the press. The KnifeKits dies and many other common ones (Tandy, USAKM, ect) use 3/8" shanks, so they won't fit that press without rigging some sort of collar to make up for the size difference. You'll also probably need to either drill and tap a hole for a set screw or pull the magnet out and put a spacer behind it to reach the much shorter dies. And you'll need to drill your own hole for the bottom die or rig up some other means to hold it. Sorry I didn't see this before you bought it.
If you can get your money back on that arbor press and want something ready to go without modding, I'd recommend just getting the arbor press and dies from USAKnifemaker. If you wanna mod the press you bought to work, I'd still recommend getting the dies from them if you haven't bought the others yet.