I've had a Solostove Titan for a while, and thought it was a decent portable biomass stove for backpacking. The principle is basically a primary woodgas burner, wherein gases emitted by burning wood/biomass are fluxed with heated air to provide a more complete combustion process, resulting in less smoke and soot if done correctly.

The Titan does an okay job, as long as material being burned is dry, mostly composed of cellulose, and the combustion process is well developed. Due to the way they draft, they work best with fire burning in a top-down manner, counterintuitive to the typical campfire model. Unfortunately with these type of stoves the fire must be fed from the top, which creates a draft problem and results in incomplete combustion of the gases, smoke, and soot. To mitigate this, if you are using the stove to cook with, you would remove the pot/pan to add fuel and let the material get going well before returning the pot/pan to the stove. If you aren't worried about smoke or sooting the bottom of your pot, then you can just stick fuel into the port at the top of the stove and let it go.

The Campfire model is a bigger version of the Titan (the Titan is a bigger version of the original, which in my opinion was too small to be of much use). The model sells for $109 on their website or Amazon, and the two pot set, when included in the order, will add another $60 to the bill. That said, the Campfire does a better job than the Titan, though it uses more fuel. It is not as backpack friendly, but I would have no problem including it if I were hiking with 4 or more. That said, it is still a very portable setup. The stove nests inside the two pots. All are made out of stainless (except the grate near the bottom of the stove, which is nichrome wire if I understand correctly), and the fit and finish are exemplary.

I collected up a handful of dry spruce twigs and some splintered standing dead birchwood from a tree in the backyard being attacked by carpenter ants. The splintered pieces averaged 3/8 inch diameter and all told I collected about 5 lbs. The pot set consists of a 1 liter and a 3 liter, both with their own lids. I filled the 3 liter pot to the line (the side of the pot is embossed in graduated marks for good volume measure) and got my fire started with some birch bark. I built my fire by breaking the splintered pieces and twigs into 4-5 inch lengths so they would fit in the burn chamber, with the biggest pieces on the bottom and building up to the smallest spruce twigs on top and the birch tinder resting on the pile. The tinder took flame as expected, and the fire got going just fine. When the system is working properly you will see low-velocity jets of flame around the top of the stove, as that is where the secondary heated air intake is and where the wood gas combustion begins. There is a chimney-pot stand that sits on top of the stove and provides a suitable volume for the gases to combust beneath the pot under ideal burning conditions. It is on a portion of the chimney (approximately 75 degrees of circumference) where the port to feed fuel is. It is big enough to allow reasonable fuel feed.

When all is going well, the fire produces a robust heat source. It took me about 10 minutes to bring the pot to the boil, and I used maybe 3 lbs of wood. As stated, feeding more fuel during the boiling process generated soot. If I removed the pot while the added fuel got up to proper combustion, I avoided getting too much soot built up. But to boil 3 liters of water in 10 minutes seemed to me like a pretty effective cooking heat source. Three liters is about as big a pot as I'd care to put on top of the stove, as it is about the size of a coffee can and not stable enough for my clumsy ways to use anything much bigger. An 8 or 10" cast iron skillet would be okay.

This would be a decent base camp stove for an expedition, or car camping, especially if you wanted a decent fire without burning a lot of fuel up like a campfire would. Dealing with sooty pots and pans is always a bit of a hassle for me in a backpack. Ultimately, I think this is a suitable replacement for a bottled gas stove. Not having to pack fuel could be a big deal, though you'd have to have a reliable source at whatever your destination might be.

I have a couple other cool stoves I'll write up reviews on here in a bit. If any of you have any questions just let me know. I realize my reviews may not be complete as I am still learning what observations to annotate.