The study found variations up to 20x in levels of formaldehyde contained in the vapour produced by some top e-cigarette products. At the low range, the levels are of little concern and barely above background. At the high range, they are of some concern. Unfortunately brands, etc are not broken down.
I have a strong suspicion that formaldehyde levels correlate with country of origin and/or quality of the liquids involved. If you stick to using PG sourced from countries with reliable certification systems I think it is OK.
