I presume the 'maintenance test pilot' was meant as someone doing routine pre/post maintenance flying and someone who can do thorough preflight and vouch for own work/practices and put his/her own neck out there test flying the helicopter.
Someone with mechanical/engineering experience especially who has done work on the heli, could know more about what vibrations, noise or feel should/should not be there, in case.
More remote ops are likely to value you more, although heli maintenance isn't the same as airliners/avionics. Canada would be good example (also USA to some degree) where AME/A&P/LAME is useful, but their flying career can suffer from being stuck in hangar, as people mentioned. I've seen it happen, when the mechanic/helicopter instructor could only instruct off duty in hangar, which limited students/hours. But the hangar work was main job with some flying as side perk.
If you do use your engineering skills as selling point, make sure you make it clear you'd not stay on if you aren't flying, from the start, if there's interest. Else I'd find it more sticky situation, agreeing to whatever to get through the door and then raising voice about not flying, which wasn't part of the initial deal. If you fly part time, you'll probably need to have other income, once you fly fulltime or instruct fulltime, the salary should be livable, ie 'award' and stuff.