From Bob’s website:
“BudBusterPro is not really in the nutrient class. It does of course have a nutrient value of 1-1-20, however when you’re applying 3ml of concentrate in 8 oz water, it’s a pretty insignificant contribution! BudBusterPro is specifically designed to increase your bud yield 20-40%, and has NO plant growth regulators.”
@BudBusterPro can explain better and a good number of OGers use this stuff now after seeing fellow OGer’s comparison grows. @JohnnyPotseed had a great thread which was mind-blowing so I decided to try it out and am hooked. Bob also has a solid reputation for assisting any grower using his product through direct communication. You shoot him a question and he’ll get back to you promptly with more information that you asked for which is a style I love. 
Seeds are significantly beefier, and same with plants and flower when you use it that way. The only “fallback” is that you need to increase your feed rate as the plant will demand more food. Once I was at 150% feed-rate and no burn, just growth! 