Garmin has a beanbag mount for the smaller portables. I keep mine
on the glareshield with a piece of anti-skid rubber velcro'd to
the bottom of the portable. There's no "head down" issue. I've
tried the portable on the yoke and really hate it because that's
where I keep the list of freqs I need.

Since Garmin has officially declared the Pilot III as discontinued
(but still supported with database) you could pick up a used one
very reasonably and use that for a while and get used to it.

Then turn around and sell it to buy something more fancy later on.