Quoted from Nokoro:The only thing I didn't read carefully enough until I got it home is that even though it has a 600 lb. capacity, it says that it only has a 250 lb. capacity if using the stair treads. I imagine that is enough for most pins and even if you go over a bit, it will be ok.
I have the exact same handtruck. I've moved probably a dozen pins now up and down stairs without a single issue. Belts are holding up well.