In terms of medical safety or purity for inhalation, I think of vaporizers that have heat exchangers as part of their design, (even the clever aluminium ones inside S&B portables and desktops!) and those with encapsulated or otherwise isolated heating coils, as being at the very top of the safety league. This includes most modern PID based vapes and ball vapes including SSV43, the E-Elev8r, and Flowerpots. Not only because the actual heat source can be run at much lower, closer to actual vaporization temperatures (because interaction with air and with your material can be much more efficient and cleverly managed), but because it isolates a constantly replenishing source of air from the coil, avoiding oxidization and potential depletion of the heater coil which you would have inhaled all your air across.
And of course in case of a fault while you inhale, the results will be more manageable.
Pioneers like the SSV makers, S&B, Vapexhale, and nowadays Cannabis Hardware (Newvape), Herborizer and many others have strived for years to ultimately offer fully encapsulated heating coils and heat exchangers for this reason to allow a safe, pure tasting inhalation and I'm not too comfortable with someone thinking, without any explanation, that they have now cracked the magic metal/oxidization/surface area formula so that the dry, energised heater element coil develops all the correct, safe amounts and types of oxidization as you inhale across it, to prevent depletion of the at times glowing metal coil, be it a plain old Kanthal wire winding or any type of wound metal ribbon or mesh.
There may someday be a certain metal type/surface area of wound element heater properly proven to be safe for inhalation, and possibly to have a system for fault situations should the coil blow or overheat, but I haven't seen it mentioned yet.
Most instant, on demand convection only vapes, or a lot of what has been recommended to you here already, use a bare coil, a wound metal energised ribbon coil, or wire mesh heater element. I'm not against the idea of portable, on demand convection only, or instant on demand convection only, if it's what I feel to be very safely performed with encapsulated heating coils (Boundless Tera) or a neat little heat exchanger (Hopper and Hopper io), both actually requiring bong or water use, the latter also having CS/reliability issues.
Hope that narrows it down a bit for you!
If you want the most pure and extremely safe inhalations, look no further than the
InVerzion vaporizer or something that has the heater coil similarly isolated from the air that you inhale, like all the big players have normally done.
I'm prepared to sacrifice a minute here or there for respiratory system safety. And since when was this herb about being in such a hurry, or instantly demanding anything at the lowest price. Chill out and take your time man! Enjoy your decision, I've found that owning just a few utter VAS busting vapes will save you lots of money and hassle for many years to come!
You won't have to spend your days waiting for the newest hot thing to launch, or for someone to knock on your door with more buys!
For a portable to out of the box, consistently, and accurately to the degree, effortlessly perform very even roasting with any amount and through water if needed, I'm with
@darbarikanada and
@Petetbay on a Mighty (or +), or I'd actually say any S&B portable with a water adapter from our very own
@Delta3DStudios
Have fun deciding.