The Universal Mobile Base has a Max. total loading of 230kg and they say will deliver only for Uk and Ireland (I’ll e-mail them to get a confirmation).
The Heavy Duty Machine Base has a Max. total loading of 250kg.
Do You know of any other substantial difference justifying the prices?
No I don’t, you could ask on one of the woodworking forums as they are often used on woodworking machines, try this one as quite a few members have them.