Now you are posting a different link. The previous one in the OP had published 5 years ago and this one was published 4 years ago.
So, they finally decided to accept xpubKey.
As o_e_l_e_o said if they have your xpubKey, they will know all your addresses. So, it reduces your privacy.
xPubKey is used in HD wallets. In a HD wallet, you have multiple addresses and are all are derived from the xPubKey.
Let's say your wallet includes addresses A, B, C, ....
I want to receive payment form Alice and Bob. I give Alice address A and give address B to Bob.
Alice will know nothing about bitcoin Bob send to me. But I give Alice my xPubKey, she can know how much I have received in address B. So, your privacy will be reduced.
I guess that's my best option to earn bitcoin easily and at low cost (1% of total transferred).
In my opinion, the best thing you can do is to not rely on a third party. Give your wage at fiat and buy bitcoin with that.