I've had an anti drain valve on my Commando for ages with no problems at all and thinking about fitting one to my 19S (1956). As the bike is used infrequently it's a nuisance to drain the crankcase before every ride, and I like the "fit and forget" nature of anti drain valves rather than shut off taps. Pros and cons?
I saw a newish product at Kempton last year, available via their ebay shop: a valve with electrical interconnection, so can’t start engine unless valve on. two versions : magneto or coil.
Enter 'oil tap with cut out switch' in eBay and you'll see the tap available from Kingpin Components - it was featured in Roadholder a few months ago.
It depends on whether you have a magneto. The mag for the singles has no earth cut out circuit so I don't see how you could fit a cut out.
They offer a points cover with a brush in contact with the points. That can then be connected to their oil tap with cut-out switch.
Definitely better than a tap with no interlock as I found when I forgot to turn the CS1 tap on. Ran fine for almost 15 miles! I was lucky, new rings and a hone got me away again although the piston is a pretty loose fit in the bore.