I can't see how that GAM split lead thingo would work.....I looked into it a few years ago, and I had my doubts about it...
So I opted for an insulated backstay which works well.
i really think a good ground is essential....the antenna could be average, but if you have a good ground it will work...good antenna and average ground...nope...won't work...'That's my experience over the last 20 years.