An easier route to establish the reason for Max Con checks on the Lynx is to look at the course of action if the engine fails the check - carry out a compressor wash.
On the Lynx you are confirming that max power measured as engine torque (with the engine not under test back at Ground Idle) is attainable within the parameters for Nh and T6, against measured air density (altitude) and outside air temperature. When it fails, it is usually a function of a "dirty" ECU.
Max Con checks are routinely carried out as a scheduled maintenance op, if engine power is suspect and following an ECU change.
The vibration and handling are simply because you are pulling max power and batting along at a fair rate of knots. Even on one engine, the Lynx is still pretty powerful at a couple of thousand feet. No reason for the cyclic to feel unusual other than you are likely to have it well forward associated with an arm full of collective. The Nr gets lower than usual, but it shouldn't be too low
Red Hot tip -When you are about to test the other engine always, always, put the original ECL back to Flight Idle before retarding the second one to Ground Idle, unless you wish to experience some new CWP captions.
And Mighty Gem is correct - Mick Dzedze knows more about this stuff than most people have forgotten, just give yourself lots of time to hear the answer.