I don't have a Sandy, but I do have a Heavy Weapons Trooper which is basically a sand trooper w/o the dirt and grime.
Wearing the shoulder pauldron limits my range of motion in my right arm. My huge gun is so awesome looking, but has to be carried around with two hands so I can't wave or high five anyone when I'm walking along. It's very cumbersome and gets heavy by the end of the troop. The backpack I got has very comfortable straps on it so my shoulders never hurt from it, but while trooping with it, it will feel like I'm not even wearing a backpack at all, but then after an hour my body starts to complain and it hits me all at once and I have to get that thing off as soon as possible! It's weird that it's not a gradual thing, it's more like: "hmmmm, my back is feeling a little stiff" and then 2 minutes later I'm thinking: "I don't care if people want another picture, I'm heading for the door to the changing area to get it off and get some relief!"
All in all, it's fun to pull out the HWT for certain events, but I can troop longer and am much more comfortable as just a regular TK.