I am sure you will be happy with either of the M140 or K140. However, bear in mind that apart from having equivalent thrust levels, they are quite different engines.
The K140 is in a KJ66 size can. It is a good bit larger, heavier, and slower revving than the M140.
K140 dia 113mm. ----------M140 dia 102mm
K140 engine weight 1650g.---------- M140 engine weight 1320g.
K140 max rpm 123k ---------- M140 max rpm 130k
The New M140x also uses the latest Xcoy electronics which includes brushless starter motor and pump etc. I believe this is the first turbine engine to offer this.
I own one of the first M140s produced and have had great service from it.. In my opinion, I think the little extra that the M140 costs over the K140 is worth it, just for the smaller size and weight.
Roger