I did some more testing. On my a500 and a1200 (both with aca1233n@40Mhz) it crashed when using the driver of the DB9 to USB device.
On my a4000t with 060 accelerator however, i noticed that everything went just very slow. Took ages to move the mouse cursor just a bit.
This was testen on just plain OS3.2 install, no other things exept for this driver installed and the needed libraries for the 060.
Btw, im not blaming anyone, i think in my case its simply the combination of OS3.2 and the software and maybe even the firmware for this particuler device.