Well it's not like you mow in the winter so you wouldn't have to put the mower deck on and off, on and off. But if you use it as a tractor in the summer a lot, and do things that would not be good to do with the deck on, then that would be a pain taking it off when you want to use it as a tractor and putting it on when you want to mow. But if you only do things that you could still keep the deck on for (like pulling a cart or something) it would be OK.
He is offering a good amount of money! Maybe you could put it towards a new mower!