I haven't however thought of using this method on an Amiga, and as you say, it is quite a good solution, especially as you verify it works.
I tested it some more yesterday, as I noticed the guy I bought it from had also put some WHDLoad games on it. I ran into problems trying to run those, but I think I was just running out of memory. Of the ones I tried, The Superfrog intro got halfway and then crashed, the main Superfrog flat out stated 'not enough memory' and didn't run, Cannon Fodder hung while loading the second mission, Buggy Boy (heh) hung almost immediately while loading, Project-X worked.

So I want to test it some more to see if this is actually a stable solution. Will move some files onto it and basically use it for a bit and see how it runs.

Another thing is that this is a little more expensive than getting an actual 4GB HD, if you can find one. I said Flash cards were cheap, but on closer inspection the cheap ones are also the really slow ones. Faster cards are more expensive. Then again, there's no point in getting a card that's faster than what the Amiga can handle, and according to Wikipedia the ATA controller in the Amigas supports PIO Mode 2, which means around 8MB/s. The more expensive cards are way faster than that, while the cheaper ones are down in the 6-10MB/s range.

The one I got is one of the faster ones, I wonder if that could be causing instability?

Do you know if this guy has any more of those for sale? I would be interested in buying it in Norway.
No idea. I checked if he had other auctions on QXL and he doesn't. I guess I could e-mail him and ask, maybe also ask where he got them.

I looked on Komplett.no, and they're selling a different type of the card there. It isn't the right one, that one is for IDE40 ports and the Amiga uses IDE44. But if they have that one, they can probably get the other one too if you contact them. Or there may be some other place in Norway that sells them if you look around.