The MAC Select Cover-Up concealer is what I have been using in class this past week. The concealer comes in a tube and is in a liquid form. MAC sells them either as an NC (neutral cool) or NW (neutral warm). A cool tone has yellow (golden) undertones and would probably use NC, while a warm tone has pink (rosy) undertones and would probably use NW. Better to try the product out to find an accurate concealer. One of the benefits in using a tube over a pot is less chances of contaminating your concealer. When using a pot, many tend to use their fingers or dip a brush after it has touched the face. The liquid form can be squeezed onto another surface to avoid contamination. of course, you can always scrape concealer out the pot with a spatula and go from there, just seems more of a pain. Anyway, the whole purpose of the concealer is to cover up skin imperfections, be it dark circles, blemishes, blue and purple capillaries ect.
One thing about this concealer is that it dries fast, so you have to apply it on quickly. Using a fluffy brush when applying this concealer, works better than flat brushes, because of the concealers fast drying property. (You can work the concealer best with the fluffy brush.)
On the MAC website it says to use the concealer pre-foundation. What you really want to do is apply the concealer after your foundation. The foundation provides coverage on its own, then you can layer the concealer on top to finish the job. ( I found the concealer to be sheer when covering blue/ purple capillaries pre-foundation.) I learned that when this concealer is used under foundation (dries fast) it can give a dried patchy appearance on the areas where it was applied. So try it on top of the foundation. Also as most concealers, it can be used as an eyeshadow base to help the eyeshadow adhere a little better - just work it in fast.
Overall. It is a good concealer, it really depends on the coverage you are looking for and how you use the concealer. Your either going to like it or hate it.
This post is based on my experiences and what I have learned in makeup class. Your experiences may be different. All in all I hope this post helps. 