There. Isn't that nice?
But I promised you stuff, in the title. So here you go.
One of the colleagues at the fair was a lovely lady who sold her own invention, a stainless steel sewing gauge. It's more or less the typical style used in Germany, without a sliding bit, which means it's resilient and will not take up a lot of space in your sewing tool stack.
Since it's made of stainless steel, you can use for marking hems and buttonholes (like you would usually do), but also for exact ironing of hems or seams. Or seam allowances - including those on curves. You can find sample pictures of this on her website (text in German).
I've watched Nannette demonstrate this, and were I a modern sewing person, I would have bought one on the spot. (I am not sewing in the modern style, at all. Which means that I also do not iron seams or hems. That, again, means that I have no use even for a nifty cool gadget like this.)
If you are doing things to your seams and seam allowances using an iron, however, this might be just what your sewing kit is lacking. Or if you are looking for a present for somebody who does modern sewing, that might be just the thing. The gauge costs 25 € a piece, plus shipping costs, and you can order it directly from Nannette by