Nelson plugs are more durable and offer better performance over most of the 1/4-32 plugs offered which nowadays is very few. The main complaint with a Nelson plug is that the hex is larger and a standard clip doesn't work which requires a clothespin style clip. The turbo plugs are more expensive than Nelson style plugs by a couple of dollars. Current cost of Nelson plugs are $8.
The Kamtechnik heads aren't a either or option. You must purchase one or the other as turbo head and a Nelson head are different threads. My advice would be to purchase one of each.
To get direct to the point though, head adapters that use standard long or shorts do work regardless of style. They generally have the engine down on power and can sometimes be problematic to get quick reliable starts.
I've personally played around quite a bit with old Cox heads that were burned out and had very successful results. I've lowered the plug and changed the combustion shape. The main problem was that lowering the plug required boring the top of the plug. This reduced the area where the wrench flats are and causes the flats to tear.