These are very nice headphones. Very, very nice. If I were in the market for another set of CIEMs, this would definitely be on my short list.
1) These are custom fit, so they'll only fit your ears. This is a good thing, as they'll be most comfortable and isolate the best this way. They should just disappear into your ears.
2) You don't lose expensive headphones. I don't know what it is, but when you're spending real money on CIEMs, you take care of them properly. You don't throw them in your pocket. You wrap the cable properly (over-under), and you keep them in a hard case when not in use. Trust me, you know exactly where that case is at all times.
3) Since these are custom made to your ear, you have a lot more input with how they turn out. I believe you can usually specify artwork for the faceplates, but I'm not sure if this particular model supports that. In general, though, you can definitely customize them to your needs.
4) Custom Art is a great company to work with, and they have a great reputation. This isn't a fly-by-night operation, and you can expect them to support you if anything goes wrong.
5) This CIEM compares favorably to the other IEMs mentioned. This is a custom fit in silicone, so it's going to be the absolutely most comfortable fit you can find. It will be much more comfortable than the LCD2 or 3 (and weight a heck of a lot less), and it will probably fit much better than the SE846 (universal fit). I would say that these should be comparable to the SE846 + Sensaphonics Custom Sleeves, which as a combo will run you about the same (retail wise). I might give a slight edge to clarity to these, though, judging by reviews (I own the SE846). As far as fullsize vs IEM, there's trade offs for both. This should be able to give you stronger micro details (because there's less volume of air to move around) and is a heck of a lot easier to drive (don't necessarily need a high end amp or DAC, although they'll help). They'll also be more comfortable. However, they won't give you the massive sound stage that an open full size can will provide -- think of an open back full size headphone as an orchestral symphony hall, and an IEM like this as a recording studio; the same performance will sound different in each venue, and neither is better or worse than the other. A full size headphone can also possibly give more of a dynamic amount of bass, although I've read that these are no slouch in that department.
6) If you're looking for a high-driver-count silicone CIEM, these should really be on the top of your list.
7) If you are balking at the price (or think that it's ridiculous), or don't want to go anywhere near an audiologist to get impressions before these can be made for you, these are probably not for you, and that's okay. if you have the money, these are a fantastic deal.