Hi Dr. Byte,
I have to tell you that I was not convinced either but the PayPal tech in Italy told me so and after some debating I accepted to make the mod indicated by them to the paypal.php, paypal_function and ipn_main_handler files in order to have them working as PRO, and it does.
The Italian PRO version is different from the USA pro version and yes it works completely different sending customers offsite.

I then wanted to have also express because I wanted to give the customers the possibility to pay without registering, but this was impossible to do because with express installed the paypal.php would refuse to install.

I then mod the paypal.php, already modded as per paypal instructions, simply commentig out the two if clauses that checks for other paypal modules installed. Installed espress, I then installed the modded paypal.php and now I have the two modules working together.

If you want to check, my site is www. acq uatua.it.
If you want to see the mods indicated by the paypal technicians, just let me know were to send a copy of the instructions.

Thanks for your answer.
Appreciated.
enzo