ORIGINAL: downunder
I've posted this photo before but here it is again
. This is the head from an OS 40VF with a long reach plug on the left (about half a thread proud) and an OS plug on the right. My preference would be for the long reach plug. Enya plugs are the same length as OS but have a reputation for great reliability.
I guess no-one has given any thought as to why the OS plugs are the length they are.
A medium length can be shimmed up or down if you "feel the need"... Five minutes, a flat surface and a scrap of wet/dry sand paper will reduce the thickness of a soft copper glow plug washer to any thickness you may require.
A short plug can't be stretched.
The long plug (as shown) is proud. I guess you could stack a couple washers and get the required height if it's that important to you.
A medium length....One plug that could be used for either short or long reach engines and still work. No need to buy different lengths....
There are those that continually bash a product for whatever reasons. Real World results prove them wrong time and time again. I've never had any problems using OS products whether it's the engines they manufacture or the glow plugs that they supply with them.
RC Universe has a "User Review" section that continually show these "Real World" results.