True... But then you have a nearly infinite supply of PS2 mice you can use on the Amiga. And they're hardware compatible, so old games, demos, etc will respond to the mouse, just like it was an Amiga one. (The converted serial mice will only work in workbench)
And you don't have to worry about things like getting old Amiga mice with bad buttons, unergonomic designs, stupid mouseballs that fall out, etc...
Plus, if you do use workbench, you can use the scroll wheel functions and extra buttons.
To me, I bought mine years ago, and I think it was a reasonable expense. Of course, if you're not planning on using it much, a real Amiga mouse may be the better choice. And either is surely better than trying to modify a serial mouse.