Hi welcome to ECF.
As far as I'm concerned, the safest HNB product is Swedish snus. The rest are pretty untested. I wouldn't go near the IQOS with a ten foot pole (personally) although I do think it has its place (like everything) in the harm reduction stable. Most other HNB vaporizers tend to be messy and inconsistent, to the best that I know of them.
Is there a reason you are considering heat not burn tobacco products? Is there one in particular you are interested in?
Anna