Vaping, like smoking, it at your own risk. It's all about harm reduction, not elimination. The only true way to eliminate the potential for harm would be to not vape or smoke at all. While we're reducing the number of chemicals from over 4,000 to, normally, between 3 and 6, there's always the potential that something in the vape isn't going to be the 100% safest because we're just not "there" yet with studies.
That said, I vape Capella's Vanilla Custard pretty much daily. I don't much care for the flavor of the one from TPA because it just doesn't match up for me. Capella's has been said to have the one or all of the flavor elements we shouldn't be vaping, which is what gives it the flavor that it has, but that's only one quick test from one lab; no-one else has stepped up and done testing on the flavoring, so right now, their flavoring is really up in the air. Many many many vendors use Capella's including, last I recall, Grants Vanilla Custard, which is insanely popular and according to his website, it's been tested and nothing was found it in.
We use flavoring in such small percentages mixed with two relatively harmless chemicals, PG and VG, whereas tobacco companies use chemistry to alter the taste, potency and composition of all tobacco cigarettes (one way, via ammonia chemistry - which increases the nicotine thump/potency when smoking - so yeah, they use ammonia). Tobacco has diacetyl in it, when we smoked, we inhaled it. For some of us, that's been 10 years, for some that's been 40+ years, so I don't feel as if the low percentages that may or may not be in the flavors we use are of the biggest concern, but that's just my opinion - I'm not a lab tech, scientist, etc.