Cross-listing and stock classes


can you guys help me understand cross exchange listing and stock classes a little better? I’ve read some sources on the topic, but I’m still not very sure.

Let’s say I want to buy Royal Dutch Shell as an example. I have 6 options - two classes on three different exchanges: RDSA.AS, RDSB.AS, RDSA.L, RDSB.L, RDS-A NY, RDS-B NY.

In case of classes, I found that there some different tax implications for A and B. Does it have some practical impact on me as a private investor who’s neither US, Dutch nor UK citizen?

The second thing I don’t understand is, that the price is very different on each exchange: circa 26,29USD to 11 EUR to 1000 GDp. How can it be? I’d expect it to be roughly equivalent. Or am I reading it wrongly?

Which one should I buy if I decide to do so?

Thanks a lot!