On average knuckleballers are quite average in term of results (ERA), but exceptional (at times) in terms of peak years, and peaking at an old age. Knuckleballers tend not to do well in hot weather as well, and of course it's a ***** to catch.
Part of the problem is there really isn't that many in recent history that have hung around for very long. I'm 26 years old and the only knuckleballer I've got to witness on a consistent basis was Wakefield(I watch RedSox games when the Jays aren't on). When he was on it was a thing of beauty but when he wasn't, it was pretty damn ugly to watch. Pretty much all or nothing, or so it seemed. There are so many variables going on. Weather being the key obviously.
I know Dickey has said he prefers being indoors in a controlled climate which makes sense, I remember seeing Wakefield pitch on windy days in Fenway and the knuckleball would give the catcher absolute fits. Passed ball after passed ball. You almost felt bad for the millionare behind the plate when there were men on-base. Going into next year, I just want Thole to block the damn thing on a consistent basis. Hitting and throwing runners out is way, way down the list for me.