I've been told, by more than one person that has one, that a 500 turns out a better product than the 100. Whether it's the extra pots, the volume of meat and the moisture it gives off, I don't know.
I'd suspect you'd get some sort of break on insurance as well because you are buring wood, instead of having compressed or natural gas around. Storage of pellets will take up less space than storing cords of wood as well, and they come in sealed bags to protect them from the elements.
As for dependability, I think you can probably order a spare controller board, and a few other parts to go along with the cooker if you are looking at an investment that size. As Bentley pointed out, there are ways to monitor the pit. If you've got a problem it's not a big deal to replace a board, pin, auger if you have to.
You can't be a real country unless you have a beer and an airline - it helps if you have some kind of a football team, or some nuclear weapons, but at the very least you need a beer. --Frank Zappa
BOOGITY, BOOGITY, BOOGITY!!!
Recipient of a Huggies box!
Shut up, and cook!!!!