Such devices get mixed reviews.  It's cheap enough, why not get one and try?
But generally, I'd recommend getting a FireWire card that directly fits whatever expansion slot your computer DOES have.

No technology persists for ever (any offers for my very expensive Pinnacle sound card, ISA slot required?)   Eventually something will come along that makes your present computer and FF400 look pretty sad, and you'll buy it.   OR, because it does everything you need, you'll keep your present system running for may more years.  Your choice.

Really, if you're going to change your computer in two years, worry about it in two years!  What you can buy NOW isn't terribly relevant.

If you're REALLY paranoid, and have only just bought the FF400, perhaps you can swap it for the USB version.   I rather doubt USB will go away.  Though you can never tell with Apple, they do like to TELL you what you can use, in two years it might be impossible to plug anything into a Mac that doesn't start with "i".   But, as they say, other platforms are available.

Oh, I?m sorry, I mean that with that maybe I can buy a expresscard with Firewire and use it with Fireface 400. I don?t know if that?s possible.

Thanks and best regards.