Living out-of and around the Defender, I've used a lot of stoves. Here are my thoughts about the MSR Reactor Stove. A summary of the pros and cons:

Pros:
1. It’s extremely fast, I boil a lot of water so this is a huge win for me. Subjectively, it takes around 1/3 less time to boil water versus the JetBoil. This is due to the more powerful burner and larger surface area on the burner interface.
2. It packs small, and as it’s wider than a JetBoil, you can pack a 220g (7.8oz) gas cylinder inside it, whereas the JetBoil can only contain a 110g (3.9oz) cylinder internally (so I always packed an additional large 450g (15.9oz) cylinder).
3. It comes with a small packing cloth which stops the insides getting scratched when the burner unit is packed inside (yes, you could easily make this yourself, but it’s a nice thought to provide one).
4. The whole unit it the typical good quality you’d expect from MSR.
5. It’s wider than the JetBoil, and that makes it easier to clean.

Cons:
1. It’s more expensive than the JetBoil ($160 vs $100 using REI prices in April 2010).
2. Simmering is difficult, if not impossible. The burner is so powerful it seems to have only two settings, off and “supernova”!
3. No piezo ignition! It’s a pain to use matches or a lighter.
4. Bigger burner means it goes through gas faster, though as you can pack a larger cylinder internally it may not be an issue.
5. It is slightly larger than the JetBoil, the diameter is larger but it is shorter.
6. It has a fold-out handle, the JetBoil is insulated so you can simply pick it up with your bare hands even when hot.
7. As the diameter of the pot is wider than the JetBoil, it is slightly more difficult to pour into narrow containers.

Cheers,
Nick.

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Nick Taylor, a Colorado Mack'em
blog | vehicles

An interesting read: thanks for posting.

Members interested in these high output, high efficiency gaz only stove could also consider these:

Primus ETA express
Primus ETA Power

I bought my Dad the latter and seems to be a nice piece of kit: a complete kit in one: you only need an additional mug, a plate and a spork and you're good to go!

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Adventure: it's an experience, not a style!
(so ride what you like, but ride it somewhere new!)