I actually have two. One is the basic chimney finder with the magnifier and then I found an immacualate prism finder with meter. CdS and works great. Its built from metal instead of plastic so its a bit heavier.
I have not found a problem focusing with this one because it really doesn't have a magnifier like the plastic one. It has a rotating glass element that I think is a diopter adjustment but I am not sure. It does appear to have some magnifying effect but I think thats from the diopter adjustment. I am not an optician so I may be wrong here.
It took me a year to find it. If you find one of the chimney finders, grab it.