I have the AT 145 and after about 10 hours of use one of the belts and the tensioner craped out. It is impossible to change the belts. Just not enough give. The reason it failed is that one of the belts was installed upside down from the factory. I would not recommend the BestCo product.
I left it too low in thick grass a couple of times. By the time I heard it squeeling, it was smoking. Lasted quite a while after that though. They are 21", btw.