No,
Does not do much for most plants, which are pretty weedy. Plants already have internal hormones they produce for these things. Adding more in some situations can help, but I think general environmental issues should be more the focus, there's no magic chemical that will help you do those
You can try it, but few bother after playing around a few times.
The idea has been around for 20-30 years for aquatic plants.
I have little issue with roots or HC using the basics, and I think no one has seen any real advantages to date due solely to root hormone additions.
Dr Kane would be the most likely person that might know.
I've personally not seen much other than what he found with Gibs and Crypts flowering.
Regards,
Tom Barr