Really? Did he give a reason? I find it works great, and the sleep feels really natural on it. There's is the taste in the mouth the next day, but I've found that bearable.
I did try diazepam for sleep before I had the zop, but found it didn't cover the whole night.
I haven't used diazepam since I started on the zop - I wouldn't like to use the two together, or if there was a cross-over period between the two - maybe this is why your p-doc won't prescribe it?