Pros: low/mid bass, mids
Cons: Treble extension, cost
I'll keep this short.
Build quality: 5/5. Looks very solid and durable. The cable seems like it will last a while, and if it doesn't - you get a second one for free anyway. The Y split is very beefy. The jack is also beefy and looks like it will last a long time. The earpieces look durable as well. They have weight to them. They look and feel expensive - and they are. They even have removable metal nozzles. No worries about breaking those tight fitting olives! Well, you might break the olives. Not the nozzles though!
Sound: These things sound great. For this portion I will mostly be referring to their sound with the blue (default) filters. I've owned many top tier universals and these are easily the best in my mind. Their main strengths are the sub bass, mid bass, and mids. The bass is the best I have ever heard from a BA IEM. They reach deep. The sub bass is very very good. It sounds like an excellent dynamic driver down low. The mid bass has great impact and reminds me of the Westone 3 without any negative impact on the mids. The mids are typical Shure. If you love vocals I don't see how you could dislike the SE846. They are pretty much the star of the show, even with the amazing bass response Shure has achieved with this quad BA. Vocals are smooth, sweet, and a bit more up front than neutral. I love their treble but I tend to prefer a laid back sound overall, especially up high. For those who love a bright top end then you probably won't like these much. The treble is there, detailed and non fatiguing but it's not well extended which can cause a lack of airy feeling up top. The white filters remedy this to some extent but they don't help the overall extension much. The white filters add some air and shimmer but overall the extension is about the same. Bass feels a little lessened compared to the blue filters. I never tried the blacks so I can't comment on them.
So, why buy them? If you're looking for a universal with great build quality, looks, amazing bass and dreamy mids - you should absolutely look into the SE846. I think they are a great step up from the SE535 LTD's. Worth $500 more? As always, depends if you can afford it.
Why not buy them? Do you love your treble? Are you a detail lover? Do you find Shure's mids to be too forward? Are you poor? If you fit any of these categories you might want to take a pass and consider the IE800, 1+2, k3003 or customs. If you're poor, you might want to consider 1. A ramen diet or 2. a job. Both will allow you to experience the wonders of top tier IEMS.