I thought I would report back:

I installed the Philips panels as replacements - that took 1/2 a day. They're thicker and stiffer than the originals, with the LEDs distributed over the panel rather than just down the sides. They're a bit less blue / more yellow in a side-by-side comparison, but not objectionably so. A bit thicker - about 35mm vs. 10mm - which was helpful in my application as the other ones flexed a bit when they got hot which made the light less uniform. The Philips power supplies have an annoying smart-arse sprung connector which is best connected on the bench rather than in the dark / above your head / up a ladder. They look better quality than the others, time will tell.

Alan