I got a 45 prism recently, interestingly enough I find it the most difficult to focus! I can see your point, however, if you require additional corrections. The problem it seems is the size, it is clearly the least magnified of all. The view is nice though, a proper prism, but I find I still prefer the 90, despite it being somewhat difficult to view through being very susceptible to viewing angle. The size (and personally I prefer the positioning) makes up for it. Of these three the I find the WLF best for focusing, and the 90 isn't that far behind actually. I'd really like a 90 *prism* finder the size of the current one! If anyone is interested I'll be selling the 45.