I've just taken delivery of 2 x 'Birth' strut tops. They're made in Italy and the quality seems good.
They appear to be made to a fail safe design? I'll take some photos of the old genuine ones next to the Birth ones.
I thought that I'd share a few things that I was told on Citroen UK Technical Courses that I have attended over the years.
Please note: This is from Citroen UK, right back to the mid-1980's, not my own opinions.

So, when the Citroen BX turbo-diesel first came out, an apprentice did a first service on one of the first ones ever sold. After his road test, there was a strange noise every time he set off from a standing. It was obviously coming from the gearbox, so we stripped the 'box down. Then again, and again and again and again. Eventually, it was found that reverse gear was ever so slightly engaging and the noise was the straight-cut gear being thrown out. The selector fork was at fault. It wouldn't surprise me if it took at least ten attempts before a cure was found...

The following week, I attended a training course in Worsley. In the late 80's I was lucky enough to appear much younger than I actually was. I would have been about 26 at the time. The course instructor thought I was about 17. He pulled apart a gearbox from a BX diesel. Put the parts in a pile and said to me: 'Put that back together'.
So I did. Every bit of it. 100% correct :-)
I bet that I couldn't do it nowadays though.

Controversial Things:
1/ All hydraulic seals on the Citroen can be reused. This was instruction from a mid-80's course and was said right at the beginning of the 'introductory' course. I followed this advice and have never had a problem with leakage.
2/ The BE series of gearbox can be overhauled whilst it's still in the vehicle. Early service manuals showed the technique. It's a simple no-compromise method and is very time-saving.
3/ in France, two unfortunate mechanics lost their lives because: One died unscrewing a still pressurised sphere on a GSA. Second died removing an airbag whilst standing outside the car. The airbag went off and his head took a sideways force, breaking his neck.
4/ A customer complained his new AX was too flimsy. 'I only hit a boy'. The boy was fine btw.
5/ Another customer complained because they'd fit his new front bumper too quickly, so it 'cannot have been fitted right'.
6/ Don't over-tighten the valve cover screws on XUD Diesels. It cracks the camshaft bearing saddles.
7/ BX Diesels with the Lucas/CAV injection pumps are faster than the ones with the Bosch pump. The instructor asked for our opinions (when you drive lots of the same car day in day out, you could tell which system a particular car had just by driving it) and then confirmed that Lucas was 'faster'. He didn't know why.
8/ Everything on a Citroen with hydro-pneumatic suspension is designed to leak.
9/ After the BX Citroens would follow mainstream design as customers won't buy 'quirky cars' any more. They justified the 'pedal-type' handbrake on the XM saying that Mercedes had used them for years...
10/ There will never be a 1.9 XUD turbo-diesel. The block is too weak. Nope.
11/ To follow when I remember it :-)