Tom, for one the COST!!!!!!! I don't have $400 - $500 to lay down for a vertical. The S9 Antenna is the best performance to cost antenna that I found during my extensive research. Also 36 reviews, and a 5.0 rating, I think it will do a fine job.
You can look at the reviews and comments. Hopefully this will change your opionion
Manufacturer instructions and antenna reviews don't mean anything in terms of signal strength.
Manufacturers tell people what they want to hear and/or don't take the time to really understand antennas. This is especially true in today's antenna market where you can read all over the internet how happy everyone is with things that radiate between 1% and 50% of your applied power. A lot of people who are end users of antennas like the popular untuned verticals don't ever take the time to compare. After all, they're looking for cheap and easy. There's nothing wrong with looking for cheap and easy and discovering that it's good enough for you.
But by far, the best bang for your buck in antennas is not a product. It's antenna theory
, or both whichever suits your skills and interests more. If you look toward theory, you should go for reliable sources and make sure that the predictions actually work, so you don't just believe some smart sounding guy with dumb ideas. And when you do experimentation, you need to be really, really doubtful that you can get the right answer, and test until there is no more room for doubt. It's too easy to fool yourself when a test confirms what you wanted to see.
We need to be more honest with ourselves in this hobby. If we want the best value for our money, we have to test and/or calculate, and probably both (as a team, not as individuals).
If we don't really care about the best, and just want to get on the air, we should be honest about that and not bother looking for the best. And we need to recognize that an antenna that wastes 75% of the applied power is probably just fine for all sorts of hams... but in no way can it be considered the best thing that could be done in most situations.
I think antenna reviews screw up people's decision process, making people think bad things work well and making them waste money. Don't forget that after you've been disappointed by three $140 antennas, you've paid for a $400 antenna... plus you can probably get a good trap vertical used for that price or less.