A problem with a lot of the systems that have "some" credibility is there is typically not any consensus, peer reviewed testing to verify how/why they work. There is a lot of anecdotal evidence, but not a lot of usable information for the engineer to take to a client.
Some of them are getting independent testing, but they are far and few between.
So the engineer has to fight the client who sees an equipment website which they think will work, or they know somebody who has one at home which seems to work, so they want to know why it won't work for them.
The engineer can quote all the science they want, but if it works for A, why can it not work for me?