Wulf Bröning's experience:
I bought one of these machines in 1993 and planned to use it in my studies. Just then Amstrad dropped all support for this machine and the only company that sold hard- and software for it was a German company called Wiedmann. They actually did sell stuff for the PDA600 till 2001 or so...
The machine itself was quite unusable, because you had to use that much pressure on the touchscreen that I was always afraid to break it. (It never did though)
The text recognition was plain bad. No matter how much you trained your writing, the recognition was slow and had many mistakes. The PC-PDA cable cost about 100 Euros and I think you could export the address files only in plain text format. Not very helpful.
One quite impressive thing though: After not using this machine for about 7 years I found it in box and switched it on. Because I had left the main and backup batteries in it all information was still there! After 7 years! Try THAT with a Palm, CE, whatever...