A comment I heard from a local gundoc about those modify gearsets (I wanted to buy one).
He said they are very good but would never beat a well-done shimming. In some cases the whole set might not fit as well as separate gears in your mechbox (some mechbox are wider or narrower then other, holes might be in oh-so slightly different places, etc). Overall a very good product but if you have time/expertise/courage you might want to do it yourself.
Just thought I'd add another opinion in, didn't experiment it myself yet.