B.M.
We have the Baby Trend Sit Stand and I love it. It really only gets hard to push if you are going up hills (a lot of them!).
I did a charity walk (5 miles) with it with my 2 boys (who were about 50 or 60 pounds together and it wasn't "that bad"). I used the heck out of it when my boys were younger!
The nice thing about it is that you can have the baby in the front and your son can walk and when he gets tired of walking, he can stand on the back part or sit down on the little bench.
I remember going to the zoo and thinking "oh the kids are old enough, we finally don't need a stroller!" But, as they get tired, they get slower and that's where the back part of the sit stand stroller is like a little piece of heaven.
I would definitely recommend it. This is also coming from the person who's husband just said "why do we have more strollers than children?" But having said that, I do think its the best stroller we have! (we have 3 kids and 4 strollers...umbrella, jog, sit stand and the one the carrier seat fits in...single stroller).
Hope this helps!
B.