I know this stuff and using it regularly already for over a decade and this stuff rocks the boat. Tho it is not a nessecity, but it definively speeds up root development of plants. Especialy seedlings or transplanted cuttings or young plants.
It contains no significant NPK's maybe a number of trace elements.. It is a Kelp/seaweed extract 100% organic and it contains mainly Hormones, enzymes and vitamines etc. B2 is one of them, for more in depth information search the Canna website. It can be used next to the regular fertilization scheme. It can be used permanently also on adult plants if you budget allows you to. But it's darn expensive.
Personaly i only use it as a startup help in the first 3 months or so, preferably a dry start.. It is not developed for aqaurium use in flooded condition. Thus for the use in this, it is purely personal experience and experiment. But for dry starting ths is absoluty worth it's money.
Canna is not the only one selling this product root stimmulators of simmular origine can be bought from a number of different brands. All are rather secretive about it's real contents other than it's a kelp extract.
My personal opinion on it.. I think it mainly aids and speeds up biological maturity of the substrate. Its organic content probably is a perfect food source for bacterial development and speeds this process up. And this again speeds up plant health and development of rizhoids (Hair roots). If it helps bacteria, it helps the plants since both are highly dependant on each other and live in a symbiotic reationship.
For example the enzyme in it is an accelerator for biological processes, not only insde the plant itself. But also in breaking down damaged/dead root tissue caused by transplanting or other yet not fully decompossed organic tissue in the substrate. This again makes this tissue earlier available for healthier biological decomposition, speeding up this process slows down or even eliminates unwanted rotting processes and or fungal development.
That's my 5 cents on it, you have to see it alllong this aley. It is not an average fertilizer.
All you can do in a home situation for testing is monitor root development.. And i did in small pots with young transpants. Add this stuff to a number of them and don't give it to others. But for the rest give them the same conditions.. Regularly turn the pots over to see when and if roots are growing out the bottom and how they look. My personal experience averagely all plants that get Rhizotinic develop stronger and healthier root growth much earlier that the ones that do not get it.
Not saying that the plants that don't get it are doomed to die, they can grow equaly healthy in the end.. It just takes them a bit longer. And your transplant survival rate might be higher with the help of Rhizotonic.