Is this unsafe? (I think not, according to the prime number theorem (PNT) there should be about 6.54*10^74 primes - a huge number - in the range as defined by the secp256k1 with the ECDSA algorithm. In other words, of all possible private keys, approximately 0.056% are prime, but only a few of these correspond to public addresses whose hash160 happen to be prime too.)