They are certainly very strong c.f. the old units! It's very hard to compress them, whereas I can compress the old units very easily.
They look very OEM, so I will try the trick of replacing just the left side only. There are (very vague, but workable) instructions included to refit all the electrical gubbins on the right hand strut, should I need to replace that one too.
Strut size and fittings look spot on - really impressed by the quality!
I've still got some refurb work to do around the hatch area, but hope to refit the glass next week.

Old OEM unit top, new one below:
