Has anyone used one of these, or something similar? It appears to be a small lantern that runs off Isobutane. Wondering how much light they give off..., roast a marshmello?

Isobutane Fuel Lamps

I haven't used that one. I have a Primus Micron about the same size.... Not as tall. Works well. The Micron is available with a glass globe or a steel mesh globe. The glass generates significantly more light... The steel mesh is more durable. The glass model is getting almost impossible to find in the US. I have the steel mesh version. It does OK for light and puts out a LOT of heat. You could definitely roast a marshmallow or heat up a tent in winter. I would never leave it lit in a tent or sleep like that however. Pretty economical with fuel and you can adjust it really low as well.

The piezoelectric ignitors quit working fairly quickly. Not too big a deal for me.
Primus does respond to customers so if you have real problems, they will help you. The lanterns take a specific mantle... I think it's a #51. Not the same as a regular Coleman lantern mantle.

Is your intended purpose light or heat? Does weight matter to your packing?

I bought a couple rechargeable LED lights. Super bright, super light, easily recharged from a small solar panel. Rechargeable LED light