Thanks for your interest in Nullo. I have a financial relationship with the Nullo company - just saying that so you can take what I say in context and choose your level skepticism - but Nullo is not chlorophyll. It is 100 mg of chlorophyllin copper complex [CCC] = a compound derived from chlorophyll and transformed into a water soluble compound. This is described in more detail on the Nullo website.
Nullo costs more than simple chlorophyll to manufacture and these costs are passed along - but you get something very different from plain chlorophyll.
Despite some modest marketing efforts towards hunters [basically a page at the website and a few bucks in Google ads during the run up to hunting season], hunters are a tiny part of the market for Nullo. Customers that use Nullo for hunting are cherished by the company but it's a small part of the big picture - that is why the bottle isn't camouflage and there isn't an giant set of antlers on the label. Nullo is primarily sold to be used in hospitals, old folks homes, by those with profound bad breath, a colostomy, incontinence, et cetera. Nullo has been on the market for over 50 years - and the main ingredient has an FDA monograph describing it as "safe and effective" for use as an internal deodorant. Hunting aside, Nullo does work to reduce odor.
But, Nullo is not a magic a bullet for hunting. For hunters, Nullo at best can be part of a overall strategy to take less scent into the field and try to place yourself and such scent as you do carry advantageously relative to the windstream and your game's likely path of travel. In that context Nullo is apparently a useful tool we are not hunting experts, but we do know Nullo will reduce the scent load you are carrying on and about your body and will reduce the scent load you puff out with every breath.
Professional hunters/guides who know a lot more about hunting than we do tell us Nullo helps them stay below the alert awareness threshold of the game longer - and that this helps them get a shorter/cleaner shot. We hear this particularly from bowhunters and folks who hunt in thick cover where even 10 yards of range reduction can make a difference in outcome.
Is Nullo a good idea for you?
if you dribble diesel fuel on your pants at the gas station before going in the field and then plunk down upwind of the game trail, I personally don't see how it could do you much good. But if you are practicing even a modest scent control regime [bathe with unscented soap, no cologne on hunt days, etcetera
] and take reasonable effort to hunt the wind then Nullo certainly has the potential to be helpful.