The description of GH3 sounds like false advertising in this regard: here's a study proving that PABA is easily absorbed when taken orally, contrary to GH3's statement that PABA isn't well absorbed:
section 3.3.9 in the following paper: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_o_058.pdf
So...what else do the seller of GH3 say that isn't true, is what I wonder. GH3 is very expensive, I wouldn't buy it without doing some independent reading.
The things GH3 turns into, PABA and choline, are much cheaper to buy.