My slave wears an eternity collar.
So I don't have first hand experience in terms of wearing an eternity collar, but I do have some experience in giving one. she shares her thoughts/experiences with Me, good or bad, so I think My perspective may give some value. I won't get into the obvious symbolism of why I gave her the collar as it seems you're more interested in the day-to-day experience of someone wearing it.
LOOKS
In terms of how it looks, it seems I may be in the minority compared to those who've posted so far, but I stand there comfortably. I love how My collar looks on her. And when it comes to day-to-day interactions, it would seem the public agrees with Me. I have never seen, nor has she ever reported to Me, a negative reception to her collar. If someone chooses to mention how it looks on her, the "worst case scenario" has been one of curiosity. Other than that, people tend to compliment it. People not versed in the lifestyle tend to compliment it as a "necklace", but they like the look nonetheless, even with their vanilla eyes.
I've never seen an outfit that it didn't go with. It goes equally well with her birthday suit as with any other outfit she has

it's a very versatile collar, even though it's on the larger/heavier side of eternity collars. I chose that very deliberately. I wanted her to feel the weight of it around her neck. It's worked out well so far.
I would also add that she wears it to work and in other professional settings. she even wore it during rounds of interviews she did to land her current job. And she lives in a country where the kink lifestyle isn't as prevalent or accepted as it is here in the US. It's never been an issue. So it looks great and works in kink and vanilla settings, professional or relaxed. I've never witnessed a situation where the collar, or its look, has caused her a major inconvenience (or really even a minor one) and she has never reported such to Me.
CARE/DURABILITY/COMFORT
It is extremely easy to care for. she pretty much never takes it off and it'll clean itself with her showering. The only thing I know that is an issue is you need to avoid salt water. So she'd remove it if she were to go to the beach or something. Other than that, it's extremely durable and easy to care for. she would go months without removing it, and it is quite comfortable.
The material is hypoallergenic, and it has not caused her any issues on her skin (other kinds of jewelry have).
"EASE OF USE"/EMERGENCIES
I allow her to keep a copy of the key so that it can be removed in case of emergencies. There is a learning curve when it comes to taking it on and off by oneself. Putting it on tends to be a bit harder as it involves tightening a small, leave-in screw. When she would visit Me, at first she would remove it when going through airport security, but I believe the last few times she did not do this and it didn't cause an issue. Going through airport security with it (on an international flight) seems to be ok. So there doesn't seem to be any real drawbacks of wearing it on a day-to-day basis, even for security reasons.
EXPENSE
Someone brought up expense, but I think this is only an issue if you're purchasing one stateside. If you live in the U.S. and are impatient, you're going to pay a lot for that. You may also have to pay a lot if you want a super customized one. But if you're willing to wait a couple weeks--and why would you want to rush a decision like this anyway?--then you can find very affordable options by buying from oversees, even when shipping is factored in. If you try to get an eternity collar off Etsy, for example, you'll be paying a very large mark-up. It would likely be the same if you buy it from any US-based kink store. It could easily cost 10x more than if you were to, say, order it from an international seller on Amazon and wait a couple weeks.
Of course, to each their own, but overall I'm very happy with the eternity collar. It has a look and symbolism that I like, it gets nothing but compliments and the occasional curious stare, and is generally not inconvenient to wear every day. My slave feels the same way, and that's not just because I like it haha. (A perhaps relevant side note: over the years I've given other kinds of collars also, from thick leather collars to day collars that look more vanilla. Every collar I've given means a great deal. But the eternity collar is unmatched and works wonderfully in virtually all settings.)