Concerning the observation that a significant number of players can hear some effect, we must be cautious. What we really know is that a number of players SAY that they hear some effect, and perhaps FEEL strongly that they hear a definite effect. But that's not evidence of a difference that others would likely hear.
And of course Doug is right that there ARE structural differences (even minor ones at times) that make a clear difference in the sound made by the instrument. Probably one reason we have so many different brands and models -- and that people have braces added/removed/moved, have lead pipes floated or unfloated, bell rims modified, etc.
There's a huge hole in things like this that confirmation bias rushes in to fill. Recent experiments with hearing the playing and listening differences between Stradivarius instruments and others (including ones newly produced) have shown a similar effect in the past ten years.
But if you can afford the (not insignificant) cost of one of these devices, and it makes you feel like you play better, then go for it. Me ... I think I'd try wrapping some solder on the horn first -- just as an experiment. But then there's the argument that $2 worth of wrapped solder just doesn't work like a $145 pair of polished plates. And it's difficult to dispute that. However, this reminds me that I need to find one of those little devices to attach to fuel lines that align the fuel molecules and enhance gas mileage. They've gotten harder to find for some reason. Thinking of putting it on my Diesel tractor.
If you want more discussion of this, there are some threads on Dave Werden's forum since some of the euph players went nuts about these a while ago. I don't recall there being any long term follow-up reports, but once the confirmation bias is gone, a certain amount of "investment bias" starts to appear.
