I bought a 2nd Octagon 20 Advance EX this past spring, to augment the one I bought last year. Overall, I think its a great product. I was thinking about buying another brand (the name of which escapes me) that has an internal humidity reservoir and cost roughly the same, but then I thought, well if I have 2 and something breaks on one, at least I can use the rest for spare parts if it can't be fixed.
Anyway, there are a couple of things I don't like about it -- 1) the rails to hold the eggs. I don't like these metal bars with the foam inserts. The system is hard to use, the foam is bulky and in the way, and it pops out of the bars. Plus, it takes up a LOT of space. My solution -- just ditched them entirely. I am now just standing my eggs up in rows very carefully, and then packing filler in any unused space. Works just as well. For quail eggs, so they don't roll, I put the mesh bag that lemons came in over the whole tray, and secure with a few rubber bands. Larger eggs don't seem to need this.
My second complaint -2) the plastic straw and silicon tubing that feeds into the incubator -- I would think they could come up with something better than that. The little plastic straw gets bent and distorted quickly, and if it comes out of the small slot, it can be hard and frustrating to get it back. I haven't found a good sub for it yet, but I'm going to look for something "off the shelf" somewhere that will work --perhaps the feed tube from a spray bottle?
Those are both pretty minor issues and easily resolved. Overall, I love the unit and am happy with it.