Good day Juha
We don't normally use any starting aids on our Listeroid other than an electric starter.
This engine has a belted on Hitachi 12V starter/generator (normally used in a golf cart) for electrical starting and starter battery charging.
This particular engine is hard to hand start when it is below freezing.
The engine does not have a COV, but it probably would be useful.
Maybe a COV on a listeroid would ease starting in very cold weather, have not tried it
(My Dursley 6/1 does have a COV and it hand starts easily in any temperature. It does not get used much, it only powers larger shop tools)
Have not used a glow plug, but I think that's the way to go for really cold starting, our small diesel truck uses glow plugs and about 30 seconds of heat will allow it to start effortlessly. they use 12VDC
Since the single Listeroid glow plug is only energized for about a minute, power use is not great.
A couple of times my starting battery was flat in very cold weather. I used a propane torch in the intake for hand starting. Still difficult to start, but it does start. I am pretty well up in years, (75+) so maybe a younger me wouldn't have so much trouble!
BTW, here's a source for a glow plug and other parts. I have dealt with them several times over the years, they are very helpful.
https://www.stationaryengineparts.com/lister-cs-glow-plug-conversion-kit.htmlCheers
Hugh