Croatian stamps (Update):
... The disadvantage is that you can buy 1 stamp per order (and hence, if you are planning to get more, you have to pay for shipping fees per order)...
It can be annoying to pay several times for shipping, but compare to the Austrian OCS1.0 it's fairer and everybody has a chance to get one OCS, instead of few people buying all the OCS at once.
Shipping fees (crypto payment shop) includes both the dispatching of the physical stamp AND the sending of the digital token. Just the transaction fees for receiving 1 digital token, cost them $2.40 (in my occasion). Further, those were sold at a fixed price compared to the CS1/CS2 (price did not change after every sale).
Overall, it was a good deal for someone willing to purchase just 1 stamp (taking into consideration the currently high ETH tx fees). Even, for 2-3 stamps total price (with individual shipping per order) was fair. As you said, it was prohibited for someone to grab many stamps. Paying 50 times shipping fees for getting 50 (let's say) stamps, add up quickly. Hence, everyone had a fair chance to get at least 1 stamp with crypto payment.