Seems I recall some old data about using "inside" reflective screens in aircraft with "plastic" windshields. Not a good idea as the heat is reflected back into the plastic and if high enough can affect the windshield. So the advise was only use an "outer" windshield cover.
Probably so. . . I sincerely doubt Twin Commander has any data. When I was looking at TBM's, this was discussed on their forum. TBM has specific instructions against both inside and outside shade covers. Of course TBM management and the dealer network is notoriously cautious and picky, but I am sure there is some science behind the recommendations against inside windshield covers.
Right now, the citation 4, Lear 60 and Meridian on our ramp have inside covers up--whatever the science says it is usually ignored. I'm fine with risking the side windows. I can't believe those side windows are subject to direct heat in a way to cause reflective damage.
Thankfully I kept a pair of my older beat up windscreen covers and they have now been duct-taped into a single piece and I secure it under the wipers on the outside when I must park outside for an extended time. On my airframe, the glass is average to below average anyway. I don't like the HOT and I am willing to risk it.