I've been using this everyday for a weeks. I do not wear this under my eyes however, if you can wear MAC StudioFinish concealer under your eyes without it being to thick/heavy/cakey...I would imagine that you can wear this under your eyes as well. In my opinion this has better coverage, I know this because I can COMPLETELY cover a tattoo on my ankle with this, set it with powder, it lasts ALL DAY. I have dry skin and found that StudioFinish was too drying, this is not drying on me. I'm really happy with this product. Now it is a bit small and I thought I would go through it quickly and loved it so much I ordered a few back-ups because I didn't want to run out however, after using this for weeks I did find that it takes so little product for what I use it for, my guess is that using this everyday, 7 days a week, it should last minimum 6 months but probably closer to 9-12 months..
On my face I do conceal a small cluster of broken blood vessels. I literally just tap it on one time, that's all it takes for me, and set it with MAC MSF Natural. I used to use StudioSculpt but because it's more emollient it does break down with your body heat and I found that I needed to touch up throughout the day and it got cakey and dry looking. I haven't had that problem with this since I don't have the need to touch up, but I will update this if that changes in warmer weather.
Overall, I think it's a great product for concealing blemishes. Under eyes? I could only suggest that you use a method that works for you or that a method that you would normally use with any other heavy concealer. Since I don't blend mine out, I just touch it on the spot with a small brush, I don't know how much it would sheer out with blending. I only use liquid undereye concealer and I never use my fingers to blend it out as it sheers it out too much so I can't comment on how that would work undereyes.
Now, as far as packaging, my concealer stick came broken, not that big of a deal, I have high-end products that break all of the time, it doesn't keep me from ever buying them again. I just keep it low in the tube. As far as the lids not fitting properly...it lasts all day on me so I don't find that I need to carry it with me so I haven't but I can see that it might fall off in a cosmetics bag, I don't know.

Unfortunately, this is being returned to ELF, with a letter of complaint. $3 or nah. Here's why: 1. Concealer stick product broke away from base, the first time that I used it. 2. Concealer itself is oily and slippery and gave me a red rash. 3. Lid does not close properly. I don't care how eager ELF may be for their production of MAC dupes, I simply wish they would come up with reliable, functioning products. Just as well I purchased the Concealer/Highlighter from ELF in the same order, otherwise I'd have been out of concealer for a special event. Shipping also took...what seemed like forever. Go back to the drawing board ELF-you can do better.