My FS-D3 arrived today and I did some quick stripping (ooh-err).
Overall impression is that it's hard to use, in the sense that it is uncomfortable. Needs significant force and then fingers can get trapped, and the blade adjuster is very hard to move. But... it works. Can strip 30awg Kynar fine, does the UTP without leaving a strand in the insulation. Not so hot on larger diameter wires where you can see the insulation being pulled apart.
I think the Knipex wins out just on being nicer to use, but this FS-D3 doesn't need fingers to hold the Kynar in place, so it's actually better for that. Blades aren't replaceable but, as already noted, it's cheap enough to replace the entire thing when they wear out (if it's still being made then, of course). For someone short of funds, they could do a lot worse than one of these.