There would be some contact between the jar's contents and the lids during the processing itself, in terms of BPA/food contact. They are in a boiling water canner or pressure canner, after all. But, it's certainly not the same as an entire can lined in BPA.....
I haven't used Weck jars. I have a TON of Ball/Kerr jars. But I did tell dh that Santa will be bringing me Weck jars this Christmas.
I think I'll start with small jam/jelly jars and then move to jars for fruits/pickles. It would take me awhile to gain confidence with canning low-acid foods in the pressure canner with them. People in Europe do all the time,though, you know?
Even if I switch entirely to Weck jars, I will continue to can some items in my Ball/Kerr jars. I give away jams/jellies as gifts - there's NO WAY I'd give away Weck jars, given their cost.
I just have no idea why they have BPA in the Ball/Kerr lids. Seriously. They didn't used to have it, why not just take it out and put plain metal lids like they used to.