A zero turn mower has one. You say your lot has a steep slope. A zero-turn mower is heavily rear weight biased and is vulnerable to overturning when mowing uphill on a steep slope. That is why I passed up on one in favor of a 48" Husqvarna.

If you feel you must have a zero turn, get the roll bar for it. There have been many injured by injudicious use of that type of mower.