In a sale I found a Bertin Course road bike with a full Shimano RX100 groupset. Price? 50 quid. Worth it or is it pig iron (says Vitus tubing mind you).

I would say rx100 and vitus makes it old rather than vintage

Sounds well worth £50. Vitus used to be a top maker long before crc aquired them

In the 60s there were various levels of Andre Bertin and they all had Course in their name.

Started at Demi Course (cheapest) Model C31 up to Course Super Professional C37. Chrome on the various ends was an expensive extra.

I had the C37 and it handled really well. It got used for all the sort of stuff I now use a mtb for as well as touring. I think the frame cost around £20 in 1963 which was quite a lot of money then.

If you have one of those most of the threads and tube dimensions will be French.

Got a pic?

Using just the name Bertin and Shimano parts suggests it’s a later model and I think they were sourcing them from the far East. I don’t know how good they were.

to be honest, for £50, so long as it works yo can’t go wrong, even if it is gas pipe.