I purchased this recently as a replacement to the concealer I was using. I was using Benefit Boi-ing concealer for the best part of a year without fail. I believe I have the older formulation thats packaged with a mirror in the lid.. Apparently the newer formulation is a bit drying?
When I first used Boi-ing early last year I loved it, I'd never found a concealer that covered so well, lasted and actually did what it was supposed to do - conceal! Everything else I tried either didn't last, or just didn't conceal anything! I have Boi-ing in #1 for Winter and #2 for Summer, I'm doubtful I will ever have enough of a tan for #2 to work properly on me, but 1 and 2 mixed together are a lovely colour for when I have a tan (ie when I apply some Lancome Flash Bronzer to my face!).
Boi-ing is more of a cream and takes some warming between your fingers (and also a fair bit of work) to get it to blend, this isn't something the Moisturecover needs at all as its a liquid. I find 4 small, lightly applied dots of the MAC S.M is all thats needed, and as I only apply it to my eye area I apply it directly from the wand. It covers really really well, it also lasts pretty well too. I find it is buildable, but its also easy to apply too much, then it just looks slightly cakey, but I guess thats possible with most concealers/products.
I basically went shopping for a new concealer as I began to find the Boi-ng a bit drying, it began to accentuate my fine lines, it settled inside them and by the end of the day my undereyes looked dry and slightly grey looking - not a good look! However with the MAC S.M the finish is much softer and it does look more moisturised.
Be aware, as with most concealers to blend blend blend if you know you're having your picture taken! I took some pictures whilst wearing this concealer and it was highly visible and I ended up with white looking patches under my eyes!
MAC S.M is £12.50 and as I bought mine online I had to pay £2.85 P&P on top. I purchased it in NW15 - the warmer toned one as the pinkness counteracts the blue of my dark circles. For reference I used to wear MAC Studio Fix in NC20. I also have oily skin, but the skin around my eye area is pretty dry :)