Last week my ND-4551A didn’t stop clicking when I inserted a disc. Since the latest Optiarc drives (AD-7190A and AD-7191A) are not based on a NEC/Optiarc design anymore, I decided to soon get myself a new AD-7173A drive before they’re out of stock. It arrived today and from the first scans that I made, burn quality seems to be about the same as that of my 4551 drive.
By the way – after fiddling around a bit and cleaning some parts of the 4551 (mainly lens and rails), this drive seems to work fine again too. But it shouldn’t hurt to have a spare drive. 😉