I must give kudos to TG for allowing upgrades on award tickets. It really is a good proposition all round.
For the pax it means that you get to upgrade at a fair (though not especially inexpensive) price. You can upgrade even if award availability was lacking in the higher class (as was my case). And you can upgrade specific legs rather than a whole ticket.
For TG, who would be carrying you in a lower class anyway, it means that they get a nice slug of revenue to carry you in a seat that would have been empty anyway a bit further forward in the plane. Essentially for the price of possible lounge access and a bit more expensive catering they get paid quite handsomely: you can buy a lot of catering for $825!
What impresses me about this is that TG have thought through the financial benefits to themselves. IME most airlines would just balk at the notion of allowing any latitude on an award ticket.