Completing a W-8 BEN does not compromise your
privacy. It is purely a way for a bank to certify that you are not a US person. It also to ensure that as paying agent it is withholding the correct amount of tax and paying it to the
IRS. The form is not even given to the IRS but must be made available for inspection if requested (not sure if this has changed in recent years but W8-BEN have always been kept internally at a bank).
The big issue is that Puerto Rico is risky. They have around 44 offshore banks and 22 of them were established in last 2.5 years. Now you explain the reason behind the doubling of the banking sector in a bankrupt country. Perhaps its just a coincidence the banks all got established in wake of
CRS coming into force also including EPB. You have limited secrecy with
FATCA (which is bilateral) and with a tax assistance request from a foreign government under the existing double taxation agreements (DTA) the US has signed your details can be obtained easily. Remember your home country can do a John Doe summons for all accounts belonging to that country that are held in Puerto Rico.