It just seems to me that having a GPS to play with is just adding another layer you could fail on. I have seen enough cockups in a 2 crew enviroment with plugging stuff into them. Never mind bouncing around single crew on a IRT at level which you could justify calling the local harbour control instead of airtraffic control. I would get failed for gratuitous use of the c word and proberly reported to the medical section for mumbling swear words under my breath when I pressed the wrong button and it went into a mode that I had never seen before.
I think everone has forgot the KISS rule.
Any extra kit you don't need for the test is just an extra thing you can fail on.
Stick the needles where you want them, trim the machine and pray ATC doesn't start moving you about for commercial traffic.
HFD I like your thinking but.. you never know with these auld dodgers I wouldn't like to risk it. Knowing my luck they would have one in thier bag or announce that they don't mind running with an out of date card as its secondary nav only "Pol hill hasn't moved for a few years now, What?" "Aye you auld bastid"
Apart from which if its a renewal the person is hardly going to want to pay extra for training on how to use a bit of kit they will never get to use again.