The problem is that there is not one Windows Cleartype. The result looks a bit different in each browser. So you need to check each browser/app in a real environment and even on different versions of Windows.
There was a problem in Adobe apps (maybe CS6) with UPM higher than ~4500. When you convert to outline it smashed all nodes higher than that down. Printing and pdf export was fine. I didn't test this recently.
The Substitution only works if you have a fi glyph in the font. The best solution (IMHO) is to have a fi that looks like a f and an i and no liga feature. Then, in the rare occasion that someone typed it directly (the fi and fl are accessible on some Mac keyboards) it will look ok. The one to many substitution could improve the appearance if a lot tracking is applied. But that lookup type is not supported everywhere.