Be sure to get the right plug boot fitted.
M10x1 plug, M14 tapered seat or M14 flat seat plug should be stated when ordering. Be prepared to read the instructions that come with it.
as for your secons question, why not ask Horizon? I can't speak for them.
If you ask me about added value:
The ignitions have some extra options like battery test and automatic shutdown that provides a lot of extra safety. Be it when standing still, or preparing for your next flight. They will not bite you either if you flip the prop in a lazy manner because they have full retard. The ignition stops the engine if it runs backwards. The ignition is potted and robust with rugged grommet mounts. The unit is LiPo ready without voltage regulator. The S-and P-types are programmable for a different advance curve to suit reso tubes. AND last but not least, MVVS has now an extended a three year warranty or 1000 starts, whichever is first.