Just a small update. I have traveled again with the Plat5. All swell. No tipping over whatsoever and great to pull along, as usual. Also, the layout of the pockets pans out EXACTLY as I had hoped. The included toiletry bag is immensely practical.
The plane was an AA MD-80. The bag did fit wheels first on the side where there are three seats but didn't fit (wheels first) on the side of the airplane where there are two seats. I had to put it on sideways which was ok because the plane was half empty.
737 and 767 were also no problem, by the way.
Till