As above, plus:
How much welding do you want to do
How rusty is it
What damage to the wire feed tube can you put up with
Is it rusty enough it won't feed through the copper collet in the hand set
Even if it does, are t=you going to get an irregular contact and thus a intermittent arc?
What class of work are you engaged in. If you're blacksmithing then it may be OK, if you are doing something structural then it's not going to fly