I ordered the thinner width because I wanted to use smaller thread for items that need a more subtle thread appearance. .3-.4mm works very well - I’m using Vinymo #8 thread with these irons and it looks great. Anything much larger than that and the tread pattern will begin to look flat when stitched (depending on how you saddle stitch), which defeats the purpose of a French style iron. I also think the widths chosen (1.6 mm for 3mm and smaller spacing and 1.8mm for 3.38 and larger), was just right since generally you want a slightly larger thread as the stitch spacing increases.
I’ll definitely still use my 2.2mm pricking irons too (with 3.38mm spacing) but some leathers/items benefit from a more subtle stitch appearance whereas others look better with a more bold appearance (in my opinion).
I received them in USA after only a couple weeks and am very happy with them. I didn’t have any issues with tariffs/customs - Sinabroks took care of that for me. I only wish Sinabroks made even more products because I would certainly buy those too. I also think offering stainless handles would be a nice addition to Sinabroks pricking iron products.