I use this over my foundation; I don't use it before foundation because this product has a rather dry, unnatural and cakey finish. That's why I prefer to go in small amounts and build up slowly so that if it begins to get too thick I know when to stop. If I did this before putting on foundation, the additional foundation will make it worst. Plus, as a rule, you're meant to apply concealers after foundation anyway.
This yellow concealer is bright & true to colour (not orange-yellow, not brown-yellow etc...), it is great for neutralising my sallow purple dark circles. However, my eye area is delicate & this concealer is thick & heavy...you know what comes next: blending becomes a REALLY annoying issue! What makes it worse is that this concealer is DRY (yep, even though it's cream formula, it is dry) so I need to blend EVEN MORE than normal concealers.
Plus, it creases in my lines & is not long-lasting despite being a thick formula. I would not like to think of myself walking down the street looking fresh and wide awake one minute then fatigued the next. The staying powder is ok to below average
I believe the one good thing about this concealer is the fact that it is yellow & DOES hide the dark circles, albeit in a drying, unnatural way...