After much searching I could find no alternative so I went ahead and bought the NorthQ enclosure. But there were a few problems and it was returned.
1) The internal width was only 145mm. A standard desktop optical drive has a specified width of 146mm. My Samsung DVD writers are 145.7mm wide and would not fit. My narrowest drives (Benq & Lite-On CD writers) are 145.2mm wide and only just fitted.
2) I tried connecting a Samsung SATA DVD writer there were problems getting Windows XP to recognise it. And when the drive was recognised it failed to recognise any discs. This was the only SATA drive I had, but I had the same problems with 3 different computers (all running Windows XP).
3) Finally I tried 3-4 different PATA CD & DVD writers (set as Master). Windows had no trouble recognising the enclosure & drive, and when I inserted a disc it was recognised. But when I tried to copy files off a disc it would stop part way and show an error message. The same happened when running the CD-DVD Speed disc read benchmark.
I have to assume that the PATA drive problems were due to a fault with my enclosure, but I cannot be certain about the SATA problems. Although both the manufacturer & vendor web sites stated that the enclosure was for SATA & PATA optical drives, the writing on the box (in Danish) appeared to say that it was for PATA HDDs & optical drives and SATA HDDs. So it may not actually support SATA optical drives (although the Jmicron JM20337 has been reported to work with optical drives).
But it was nice to have an internal PSU and the fan was fairly quiet.