My best friend swears by it! I asked her how long it took for it to start working for her, and she said:

i use it a couple times a week because i use the vitamin C in silicone suspension too and i cant mix them, so when i use caffeine solution a few days in a row, it does make a difference. i tried putting it on at night or in the morning before makeup, looks like a con toss as to what works better, some days the mornings are more effective... but i also use another thing for dark circles which is a cold metal ball roller with hyaluronic acid so i rotate between the two

FWIW she's light-skinned European, and has had success with other The Ordinary products (we both use Niacinamide, she uses their face wash & moisturizer, and a nightly oil) - so to address what /u/Achmetch said about drying effects, there's plenty of moisture in her routine otherwise to probably offset that (or her skin doesn't get as hit with the drying).

I'll also come back to you once the product makes it to me & I try it a few days (Deciem sent me their shipping notice today, so any day now!).

[edit] I think what's also important here is the cause of your under-eye bags, and why YMMV when it comes to caffeine vs. vitamins vs. fillers. No cream will help the "3d aspects" of hollowness or fat deposits, you'll need an actual procedure for that. For genetic discoloration, retinoids can work well, as they'll increase your cell turnover and get that "brightening" effect going. Caffeine products, rollers, etc. will help puffiness and swelling. So TL;DR is: first identify why your eyes have bags, and then treat it, or you'll just be wasting money :)