Just adding to the discussion, I think that the interior ones are a right pain! Not easy to fit, I witness people struggling with them. Take up space visually, clutter the cab.
We have an external Silverscreen brand from Yorkshire, not cheap, but we bought it because it seemed to be the most popular.
An advantage of this brand is that the windscreen portion can be folded down during the day in summer to reveal the view or to allow light in during the day and put back up in the evening. Very simple quick fit.
Another advantage is that for full timers staying put for a while the inner blinds can be closed which makes the cab brighter and more homely, uncluttered.
Ours has survived two years of extreme summers, 45 degrees in Italy, while our Kampa tent totally persished.
UV may still perish it through the windows would it not?
I do get the UV issue, but I’d rather replace the screen occasionally than have internal thermal blankets! Most use messy suction caps to hold them in place, so the thickness becomes bulky. They never look neat?
As an aside, the heat last year melted our van awning while it was rolled up! The aluminium outer panel got so hot on the shady side (North side up here) that the fabric against the bar shrank over 100 mm!
Yorkshire, farmyard pitch, somewhere?