One more thing, I am assuming now that I need the 1 1/4 diameter clamp instead of the 1 1/8 diameter clamp? I guess performance only carries the latter. Is my seat tube on a trek 1200 1 1/4?
so... now before I make another mistake, what is the difference between these two deraileurs except the price:

https://shop.sunrisecyclery.com/item/10389/

and the cheaper seemingly the same:

https://shop.sunrisecyclery.com/item/10833/