I've cooked on one and although they really do cook food quicker, I found the results lacking.
I did a fairly big cook a while back (my first big one) and used another guy's Orion Cooker and an 18" WSM and my ECB to cook up some butts. If I recall, I had 3 on the WSM, 2 on my ECB and 3 on the Orion. The WSM and ECB cooked at the same rate and took the "normal" amount of time, like 10-12 hours and put out typically good stuff. Following the instructions on the Orion, the 3 butts only took about 4 hours to cook and even though I used wood chips for smoke inside as the instructions suggested, there was really no bark to speak of. The meat was indeed done and tender enough, but I didn't get any bark and, in fact, the outer layer was gray and soft.
It's basically an outdoor, charcoal fired convection oven, but since the charcoal is placed OUTSIDE the cooker on that ring, the inside really doesn't get any charcoal flavor and only the smoke from the chips you put in. Perhaps I could have put in more chips, but for the dough they want for those things, I'd just get a WSM. Heck, even for that sales price, I'd get ECB's and modifiy them before I'd get one. Just sayin. The ECB can really put out some fine Q with a little help of mods.
18.5", 22.5" OTS
Large BGE (chambersuac's)
The Fiery Furnace (chambersuac's)
Big JT's Smokin' BBQ Competition Team