The adapter lifts the stock mounting point of the cable putting more pressure on it where it passes through to the chassis. This also causes the shifts to be stiffer and harder. At least one member with an adapter had his shifter cable break and they are expensive to repair.
I heard enough bad things about adapters to scare me away from them. Some people have no problems and love them, but I didn't want to risk being the one who did have trouble.
Shortening you shift lever is not exactly the same as getting an adapter, but the results are comparable. A shortened shift lever gives you shortened throws, but they aren't notchier or stiffer. Do a search in this forum. I and several other people have posted our reviews. It's a very easy mod to do also.