If it has Greenteeth, buying a set will be very worthwhile. Fast and easy to change. Teeth are consumable. Pockets, not so much.
Its like using your own sharp sawchain over a dull chain for free. If you own a stump grinder, you are still paying for teeth. Rental companies don't charge for dull teeth, but they might for broken teeth.
Soil Type is very important. If you're in rich topsoil (some housing developments have 6" of top soil on top of native soil), you can grind through it without dulling teeth like glacial outwash soil with lots of river rocks (14,000 years ago, my area was bedrock under lots of ice).