I've only ever used GH Liquid Silicon, this was last year when I did a photo run. Everything that could go wrong, went wrong, including a close-encouter with a fire-hazard. I am amazed they survived and I am pretty confident the silicon contributed. I definitely saw a much bigger stem. I had bad pH problems because I wasn't using it right, and abused of it. Despite almost killing the plants twice, I got a pretty nice yield :joint: (nothing to do with the silicon itself, mind you)
So all in all, in decent hands I believe will make a very significant result. All reports account to that. I will deff be using it next time round.
Just remember that silicon is very toxic, and I think remember reading it can deposit in the bud when they start packing sugars. So stop using it in early flower