I used to run a D20 Star Wars campaign years ago, and I created some At-St walkers for it. I created an original piece and then made a mold of it and created a few pieces. I used my AT-AT model kit and the chicken walkers with paper miniatures and they worked well. This was before I got addicted to plastic Star Wars miniatures.
I didn't buy the At-At miniature, but I've been using this kit with the miniatures. Even if it's a bit small to be used with the miniatures, it looks ok if there's no other vehicles around, but even if there is it's still better than nothing.
And, the model AT-AT looks better than the miniature, which looks a bit clumsy IMO.