Rootbastic is the partner product to the ever popular Bloombastic from Atami. Atami state that it's a "Super concentrated root stimulator with a combination of high NPK bio stimulants and Bio minerals". It's actually one of the best root stims on the market, and one of the cheapest when you look at the dilution rates.
You use it from when your plants have 2 inch long roots for a 3 week period. It will raise your EC slightly so put it in to your nutrient tank before your base nutrient, otherwise the EC will be on the high side. In our experience you will see very strong root growth within days and after 3 weeks the plant will be set up nicely for it's flowering stage.
Highly recommended, excellent value for money.
The Rootbastic website has a pretty comprehensive FAQ page, take a look here.