I bought this Innisfree product during a sale and have been using it. Surprisingly, it's not as oily as I expected and feels a bit potent! I previously used Dermafactory's 0.03% retinal, which was just greasy without much noticeable effect. So, I applied the Innisfree product without fear of irritation after purchase. The Innisfree product has a very low retinol percentage, around 0.01% I think. However, it's stronger than I anticipated! I felt a slight tingling sensation when washing my face the next morning. On the plus side, I've noticed a reduction in excess oil on my face when I wake up in the morning.
There's more irritation than expected. The value for money isn't great when it's not on sale. The concentration is very low.