I have fixed several that were leaking, this was because of workmanship.
I my area the guys that use California valleys seem to put out lower quality work in general.
Because of this I equate a California valley with sloppy workmanship and a California valley as being a shortcut.
Properly done they will work fine, but to do it right involves cutting the shingles.
Not having to cut the shingles in the valley is supposed to be one of the features of this type of valley.
It is faster.
Also the shingle that is layed in the valley creates a small hump.
As mentioned in my previous post they also encourage smaller staggers depending upon the pitch of the roof.
As the pitch increases the stagger gets smaller.
Unless you are requesting open metal valleys it would be best to let your roofer do the type of valley that he is comfortable with.
This is just my opinion and others experiences may differ.
I prefer a closed cut valley or open metal.