I just moved up from a 10 to a 12, and the size and weight differences are significant. I thought the 10 was heavy already, and the weight of the 12 was my major worry. Last night I set them both up side by side to compare. Viewing was really poor, but oh well.
It takes significant strength to move the 12 around. It also weighs enough that it can decide on its own where to go, and there's not much you can do about it. On the other hand, once you get it to the tripod and liiiift, there is a nice smooth surface to put it on (unlike the 8 and 10 tripod, which has the bolt sticking out) the tripod head is also the same diameter as the round part of the drive base, which makes centering the base over the bolt a cinch.
The giant field tripod itself weighs a lot, so that is another consideration. This is a telescope built for two people to move - the fork has four handles rather than only two like the 8 and 10 models.
Hope this helps!