I picked up this little gem out of curiosity; I usually use MAC, Bobbi Brown, Laura Mercier, Chanel, Tarte, YSL and ByTerry concealers. This one, however is garnering use and praise from people like Lisa Eldridge, the Pixiwoo sisters, and when that happens, I pay attention.
I have been trialling it every day for the last week on top of various different formulation and finish foundations (Illamasqua Skin Base; MAC Face & Body; Chanel Perfection Lumière; a random BB cream I got from Korea).
This is actually a great concealer! No caveats, ifs, ands, buts, or maybes - it's just really really good. It's a medium coverage; for reference, it's a little creamier than MAC Select Moisturecover (more info here) and also slightly creamier than the Chanel Long Lasting Correcteur Perfection. It comes in a similar shaped container and doe-foot applicator as those two products.
I didn't find it particularly drying or creasing - but like most concealer products, if you put too much of it under the eye or if you don't take out any creases before you set it with powder, it's can crease.
It doesn't have any strange smells which is a bonus; I hate makeup (especially near my eyes or sinuses) that is scented.
It has good coverage, both for blemishes and under-eyes. It's matte (as it should be) and has no shimmer, but it does have a small amount of inbuilt luminosity, so it's not a "dead" looking matte.
It applies and blends well with a flat brush, fluffy brush or fingers.
It is ridiculously cheap, around the €4 mark (approximately) and is available in drugstores around Ireland.
I've found that it works on top of all the foundations mentioned above. I've found that it lasts the day no problem. I've found that it sits alright on top of the correctors I use (mainly Tarte, Illamasqua and Bobbi Brown) - probably not the 16 hours Collection 2000 has claimed, but I don't want the same face on 16 hours later anyhow.
It's water resistant and transfer proof - definitely, I haven't found it budging much (and I'm a face-toucher).
It's oil free and purports to work on all skin types, however I've only tried it on mine thus far (combination, "not quite mature but getting on" skin).
The only downside, and it's minor, is that there are very few colours from which to choose (Deep, Medium, Light, Fair). The lightest colour (01/Fair) is really a very pale ivory pink. 01/Fair and 03/Medium are more pink-toned; 02/Light and 04/Deep are slightly more of a salmony shade - but these are concealers not corrrectors, so you may still need a corrector underneath (if you don't use a corrector already, you won't need one with these either).
For the record, I've been I wear 02/Light and am about 20-30/in Chanel foundations, between a C2 - C3 in MAC Face & Body and I correct undereye circles with Bobbi Brown Bisque or Illamasqua Cream Pigment in Emerge (see here for more info), and I've found that 02/Light is perfect for me.
Upshot: I can't recommend this enough. I will most defintely be re-purchasing.