I've got two sets of gimmicks and they both work flawlessly. I do understand the lack of spread that is mentioned as I ran into at first my self.
The answer, however is VERY simple and you can get predictable results every time.
Hint one: try adding a touch more, not less pressure to the cards when you fan them. This will force the gimmick to grab. Hint two: look at your spread and if you constantly get one card that wants to spread unevenly, just change the order of the cards. Place that one in the middle. Hint final: At times I find it isn't the gimmick but rather the standard cards that may wear a touch from friction of spreading. Use new ones. I always recommend a magic finish but it's not required.
Hope this helps. The trick has become a staple in my routine.