I have the Max G2D. It becomes critical on a 10% incline. The speed should collapse to 5 km/h and possibly even come to a standstill. It is very important that the tyres are well inflated (check every few weeks!). I would go to the upper limit with the pressure. The rolling resistance should not be underestimated. A well charged battery is also important. Especially in winter. The brakes on the Segway are not that special.

I have a Segway and a Vmax. I'm also 100kg and the Vmax is a lot stronger on hills.

I would look at vmax. They have real power.

450 watts is better for climbing