This has to be the first of the long fuselage Merlin/Metro II family and here visiting Perimeter Aviation while on a sales tour. Early Merlin IV are notable in that they have round windows. Later they had the 'curvy rectangular' ones as per the Metro II for production commonality. The registration N5291M was later used on c/n TC-202E and maybe it is this same airframe as the 'E' indicates a switch from Merlin to Metro on the line. Since TC-001E would have looked odd plus it would need major work to change the windows, maybe they went to the later number '202'. Just a theory.