Reimann P20 is very very effective, but (I recall from previous threads on here, IIRR) it only blocks UVB, not UVA. I'm slightly dubious about these sunscreens that filter by means of some kind of chemical reaction rather than a physical block.
Still, due to last year's non-Summer, I still have two bottles of P20 to use up.
Query for any P20 users: I have 2 unused bottles, no use-by date on either. I presume the date is on the outer box (binned). If any of you have the box to go with yours, how far hence is the use-by date?