Dennis,
I suggest you speak with others who have the Skywatcher ED 120.
A quick look suggests that the ED 120, at close to 14.5kg, would be near the top end of the carrying capacity of the Ioptron Mini Tower Pro, listed at 15kg.
If you are planning on AP you need to factor in the weight of your imaging gear as well.
My very limited experience would be that the supplied tripod might be found wanting.
I reckon other users might suggest a larger mount.
Cheers
Chris