How to politely reject product recommendation from a financial advisor who is also a friend?

Say you don't have any more spare cash to plow into more plans. It sounds like you've already bought a number of plans so it is an acceptable reason.

You seem to have already rejected him due to your beliefs.

Have you given him a chance to explain why his still recommending?
If no, consider that. After which you can firmly reject without having to be polite.

If you are plain not interested, just be firm.

Friend is friend. Work is work.
He is advising you as a professional.
Rejections are part of being professional.