So the transparency node is supported for grayscale but not for colour.
That was not so clear in the description:
Color input is now supported for the Transparency BSDF node
I had a mix shader with diffuse colour and Transparent colour in Blender 2.79. I have set the transparent colour to white and strengthened the diffuse colour a bit so it works well now.
I tried the new Built of Blender 2.8 the transparency node works well. I think it’s nearly time to make the full switch. The 2.8 built of today is truly awesome, a lot of issues (with weight painting and so on) of last week have been fixed and the new interface changes are fantastic!
I understand that consitancey with the Eevee nodes are of most importance now.
Thanks for your quick reply,