The one I have works well with a 14" monitor - or indeed, any monitor displaying at 640x480 resolution. I also have not experienced any ADB anomalies. So it does just fine for its intended uses, and is one of the most useful bits of old kit that I have.

I will, however, now definitely keep my eyes open for a Dr. Bott Moniswitch in the light of the comments made. Thanks. A couple of the switches have been on eBay lately, but only the two connection units, whereas I want one of the four connection units.