Yard Guy wrote:
....

What's the verdict on these things? Are they effective?

I've seen no independent testing results that indicated they're more
effective than alternatives tested--which is pretty much why they're not
particularly widespread; it appears that most of the glowing
testimonials are either sponsored "research" (read advertising hype) or
self-justification of the $$ spent to avoid admitting have been suckered.

It's been a while since I looked but google found several studies a
while back from various land-grant universities, etc., that concluded
they're of minimal help if any...

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