We do use them for leveling and have done so since our first Oliver bought back I early 2008.
Advice: Chock the tires fore and aft, then unhook the trailer and move the truck.
Raise/Lower the front jack first to get the trailer level front to rear.
If the trailer is not level side to side, use the jack to raise the low side to level. Then lower the opposite side to stabilize it.
Make sure you place a block between the jack foot and the ground. That way when you forget to raise them before driving away, you won’t ruin $1200 worth of jacks.
Routinely check the bolt that holds the foot plate to the inner jack tube. If this bolt works loose, you will lose the foot plate that will cost you close to $40 to replace.