In terms of randomness, I'd say that it's on the secure side for concatenating uRandom and its "Audio-based" entropy generation. (audio_randomness.py)
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 encoded WIF has compressed pubKey flag to be compatible with SegWit. (K or L - WIF)
But that's not currently supported by clients supporting mini private keys which automatically assume that it's associated with an uncompressed public key.