That's definitely a decent slim line fitting, ideal for kitchens and less noticeable than the PP1-8s that I used back in 1995!

No it is not. While made with the expected 90's quality, it is still a single use disposable, with tube in contact with fully plastic housing that will discolor and non replacable hardwired glow starter inside. Any proper fitting is better than this

That is the trouble, anything with the tube directly against plastic is really only good for one or two tubes depending on how long they last etc, especially if putting mag gear right onto the plastic too, as we unfortunately found with Fern Howard...
A bit of sheet metal behind the tube and it being adequately spaced from the cover would help things somewhat though. For that matter I wonder if running something as simple as a strip of aluminium tape behind the direct area of the tube and its cathodes would help preserve some plastic fittings/trays a bit longer?

Definitely would, but what about the diffuser on the front ? It would still need a little better spacing from the tube, or to be made of glass. A 8W choke does not dissipate a lot of power anyway, just making it a bit longer (so larger surface area and lower loss) would keep its temperature down

I think that in terms of the design asthetics, it looks great. I have a similar fitting which is also made from plastic which I've had for 15 years, so far the plastic is holding up well, even with the UV from the tube and the close proximity of the tube to the plastic. Have them as under shelf lights in my living room, they are on daily. I wouldn't expect it to have the longevity of a steel fitting though.