In terms of randomness, I'd say that it's on the secure side for concatenating uRandom and its "Audio-based" entropy generation.
And it doesn't stop there since the result is also combined with timing-based entropy.

As for the generation of the mini private key;
It's using a 29-character part of the base58-encoded entropy appended with "S" which isn't too bad considering there's no standard on generating mini-private keys.

What I'd like to see is a modern version where the derived WIF is with compressed pubKey flag to be compatible with SegWit.
But that's not currently supported by clients supporting mini private keys which automatically assumes that it's associated with an uncompressed public key.