When it comes to the average consumer, however, I can't see this ever taking off for a couple reasons:
1. Smell is one of our least important senses - while it might help immersion, very little of our information about our world comes through our noses, comparatively speaking. There are many, many subjects that might be improved to provide better immersion than scents, which are, ultimately, optional.
2. On a related note, smell is a less developed sense. The amount of bandwidth our noses provide is massively limited, unlike audio or visual effects. Additionally, multiple smells in a short timeframe will interfere with each other, preventing more complex arrangements. This means there is less design space for creators to use and consumers to experience.
3. Because of this, most people's olfactory needs can be satisfied with less difficulty at a lower cost. Rather than purchasing an expensive device that requires power and refills, you can just get an air freshener. Novelty and variety in smells is much less of a priority than simple maintenance of a pleasant base standard.
In the long term, I'm sure smell simulation will be achieved for VR-style experiences - but almost certainly not through these devices. As long as there's no simulation of motion, or, less importantly, touch, immersion will not be complete enough for lack of smell to be a notable factor. I expect that all three of these senses will become available when we're able to manipulate them more directly - attaching to the nerves, or perhaps via neural implants, as any physical measures for motion or touch are crude and generally ineffective - and that olfactory devices will see negligible success in the meantime, until they're obsoleted.