Regarding the security when using the public key for message encryption:

The security of the ECIES encryption is equally strong as the ECDSA that bitcoin use.

It is possible to estimate the strength of the encryption in monetary terms.

This is an address that contains 92 000 bitcoins:
https://blockchain.info/address/3A1KUd5H4hBEHk4bZB4C3hGgvuXuVX7p7t

The address is reused, money has been sent repeatedly from that address.
This means that the only thing that protects these 92 000 bitcoins is the Elliptic curve.
(When a message is signed the ECC public key is revealed)

The ECC is in this case able to protect 92 000 bitcoins.

If your encrypted data is worth less than 92 000 bitcoins it is safe.