Any portable "on demand" vape is essentially a "vaporizer one-hitter".
For me a one hitter is almost the opposite of on demand. One hitter, it just one hit (a short session). You put it at max then draw one time with your vaporizer. Then you get nice thick vapor and your ABV are hopefully a nice even brown color.
On-demand, is the contrary, you extend your sessions over many hits, possibly many hours/days.
For example, the MFLB is clearly a on-demand vape but not a one hitter. It's not a one hitter because it's conduction and you must mix between hits. Put it at max temp will only roast one side of the load. But the mflb is a great on-demand vape. Put 0.1g in your box and you can use it every now and then for a full week!! Taking draws only on-demand. It can do this because it doesn't cook your herb when you have finished drawing and heat your herb very quickly when you start drawing. So it never vaporize your herb more than you need to take a draw.
I'm a big fan of on-demand vaping. The real opposite of on-demand vaping are session vaporizers like the Pax for example. My desktop E-Nano is also on-demand because it doesnt cook your herb when you stop drawing. The grasshopper can be used in both ways. Both on-demand and as a session vape (although it could get hot as a session vape). I plan to use it as pure on-demand vape. Buzz made an experiement showing us that the grasshopper definitely doesn't cook your herb between draws
when you turn it off after each draws (EDIT: actually Buzz showed us that the Grasshopper doesn't cook your herb even when you keep it on at max temp!!. So it's a pure convection vaporizer. Only the action of drawing your Grasshopper bring heated convection air to the herb to vaporize it)