I think all riding mowers are recommended for no more than a 5% slope.

The accident occurred because your tractor stalled, not because of the brand.

Buy one of the higher quality Toro mowers.

I happened to use my Wheelhorse today and there is a sticker on the floorboard with warnings. No more than 5% sideways on a hill, no more than 10% downhill and no more than 15% uphill. All percentages are a departure from level.

A 5% slope is only a departure of 5' in 100', not much of a slope compared to what I see people cutting with riders. I guess this is why there are so many accidents/injuries. I cut a 58% slope (30 degree angle) ditch bank with my push mower every time I cut grass. This is way over the mower specs but as long as it doesn't start sucking oil I'll do it.

Riding mowers by their very design can be safely operated on only the shallowest of hills. The wheels are close together and much of the mower rides high so it seems almost designed for tip over. I would strongly suggest that you receive some instruction on how to operate a riding mower safely. The owners manual typically has a lot of information in that regard, but that information is apparently not available to you. You may also have to consider a walk behind mower for steeper situations.

I'm glad you were not more seriously injured.