I bought the Caffeine Solution (for eyebags/dark circles), Buffet (general serum full of peptides and lots of good stuff). I've also started using a Hyaluronic serum which I got from La Roche Posay but had forgotten about.
I put the HA first, on a damp face, then the eye serum, wait a couple of minutes then the Buffet. Couple of drops of each is plenty.
I plan to buy a few more things soon, (moisturiser, Rosehip seed oil and a Vit C product. The idea of the range is that each product does specific things so, instead of slathering on one product that claims to do everything, you layer specific serums that target specific issues you want to address, acne, pigmentation, lines, ageing etc.
The Buffet is the most expensive thing and that's only £12.90!! Most are about £5 - £7 each, 30ml bottles so when you're only using 4 drops a day, it should last a long time!
People rave about the stuff, a lot of it's to do with price, but also the fact that it's pure, because they're not trying to mix things and incorporate into lotions etc, so they don't have to use "filler" ingredients which don't do much for your skin. They use the active ingredients that are meant to work. Also cruelty free, vegan, no parabens etc.
Lots of videos on YouTube and Victoria Health or Beautylish are good sites to look at, as well as the Ordinary's. I ordered from Victoria Health and the order arrived in 3 days. Apologies for the humongous post!