I've been a loyal Oakley user for many years so I was very excited to see what other goggles such as the I/OS's had to offer. Overall they are a good goggle and would recommend them. Here's my breakdown:
Lens: Quality lens that are clear and accurate. No fog problems. The lenses that came with my model (ignitor mirror and red sensor mirror) cover a decent spectrum-good for bluebird days and ok but not great for low-light conditions. Field of view and peripheral vision are very good.
Fit and comfort: As others have mentioned, the I/OS fit is for a smaller face. If it's any indication, I wear a size medium helmet and these fit my face pretty well. Any bigger and I would opt for the regular I/O goggles. I use a Giro helmet and the interface is generally good. They usually sit together nicely, but if I don't make sure my helmet is sitting squarely on my head, the dreaded gaper gap rears its ugly head. They are comfortable, but got itchy a few times (but not so much that is was distracting).
Ease of Use: Switching the lenses took a little bit of practice, but once you've got it figured out, it becomes quick. I don't find the clip on the strap to be particularly helpful, in fact it's kind of annoying when it comes undone in transport. The adjustable sliders are kind of a pain to slide around and adjust. Not too much of an issue if you keep the strap sized for only a helmet or only for your head, but it's annoying if you switch between the two frequently.
Quality: Both the lens and frames seem to be rock solid. The lens are still scratch-free after a few bumps and a little bit of carelessness on my part.
I'm unusually very picky when it comes to goggles, but I think these are a good high-end option. They have their shortcomings, but they are one of the best goggles you can buy, without question.