You should be careful when using word like quality in this context. Some might think that by quality you mean any kind of statistical property. E.g dice rolls g

You should be careful when using word like quality in this context. Some might think that by quality you mean any kind of statistical property. E.g dice rolls generated by either of them are somehow statistically different, which they are not. What does this mean in practice: If I give you 10 10MB files. 5 of them created with urandom and 5 of them created using hardware RNG there is practically no chance that you could differentiate which came from which, barring knowledge of the urandom entropy pool. But it is true that HW RNG could be useful just to keep CPU load down. By now we know that those are backdoored by NSA, so you should still use /dev/random as a source for private keys. So HW RNG is useful just to keep the load down. Not to avoid any attacks. This is so important that I'll have to repeat it again: The only difference between urandom and random is that urandom is theoretically suspectible to an attack which could allow prediction of the output values if the attacked knows the internal entropy pool state. The statistical properties of both are the same.