I disagree with this idea, there is a substantial difference between the two. VG has a heat exchanger where the DV depends on stored heat for the hit. This means, for instance, you can replace the heat during the hit. This keeps the delivered heated air at at even level rather than the ever declining DV. DV forces us to start the hit hotter to ensure it doesn't poop out too fast, VG you approach from below and therefore don't need this over shooting?
The idea with candle flames being lower temperature is also a bit off. The total energy available from a given amount of gas remains the same in normal conditions. This is the reason your home heater is basically a candle flame, if you got more heat from 'torch flame' the cost of fuel would make that the system we'd demand. The rub is of the two reactions involved (burning the hydrogen giving water vapor and the carbon one producing CO2) the water one happens first meaning if you cool the process, the carbon doesn't convert not the hydrogen. This can cause solid carbon to deposit as 'lamp black' same as collects on the glass in kerosene lamps. No strange/toxic compounds are possible. Gas, containing carbon and hydrogen only, is the only source of chemicals. Remember we vent gas stoves and wall heaters into the room we live in, and have for a very long time.
Nothing to fear, IMO, but if you let candle or other 'yellow flame' sources like hemp wick get too close to the heat exchanger it will 'soot up', eventually blocking flow. There's a procedure for cleaning the exvchanger with a touch and vacuum cleaner.
Of the two, I think VG gets the nod on many fronts. DV is, OTOH, easier to use even if only the single way it's designed to.
Regards to all.
OF