Another 3 wheel driver here (prior to my power chair)
As my friends here have said, 3-wheelers tend to have a tighter turning radius, and they move through the queues a bit easier as a result.
Personally, I have used (my own) 3 wheel device for more than 5 years on a daily basis, and never have had it try to tip over yet. The biggest safety tip is to mind your speed - if you try to turn (either a tight, sharp corner, or a wide, sweeping turn) while going too fast, it would indeed be possible to tump over. That is easily avoided by minding your speed.
Another potential issue to watch out for is to make sure you cross the tracks in Main Street at MK at an
angle - you don't want a tire to get caught down in the groove; it can easily result in an accident.
The thing that can make a 3 wheel device feel "tippy" is the center of gravity. As long as you are using the device as the manufacturer intended, there should be no problem with that getting so far out of balance that you have an issue.
So, don't try to race other
ECV drivers for "pinks or drinks" and don't go jumping off curbs like some kind of tiny Evil Knevil, and things should be fine...
Let us know if you need any more information about using a
scooter at WDW!