That isn't really true. I am sure Catweasel MK4 has great potential and the hardware is great, but there are virtually no drivers for it. (I'm talking Windows here).
It cannot write Amiga floppies:
Ok, it can write savedisks and data disks, but it seems it cannot write any bootblocks. So transferring a game adf image to a real amiga floppy is impossible.
I tried writing a bunch of games, only to find them unbootable on my Amiga 500. I tried to install a new bootblock with my Action Replay, but it just gives a checksum error. However, if I format the floppy on the Amiga, it can install the bootblock. The only bad thing is, then you don't have the game on the floppy anymore..

I've tried to write many games to floppies and then read them back in, but Catweasel always gives error messages on sector 2-20.
The passthru doesn't work:
You are supposed to be able to read Amiga and PC floppies through for example Windows Explorer. This is not possible. A: becomes unavailable when you install the Catweasel drivers. I cannot read PC floppies anymore, and Amiga floppies only as images.
Reading/writing C64 (1541) images doesn't work:
At least not for the people I've spoken to. I've never tried it on my own Catweasel.
I have tried to contact Individual Computers four times(!) with questions, but they have never replied.
To sum it up, I would never have bought the Catweasel MK4 if I knew about the lack of software support and device drivers. You get a very basic image tool, but it's almost unusable, because it doesn't even have a retry option, so reading your old floppies from the nineties becomes impossible.
If you're thinking about buying one, I suggest you wait until some proper drivers are released. It seems Individual Computers are more interested in making lots of new products than actually making the existing ones function properly.