I’ve been meaning to start a thread here asking about the horizontal buttonhole. I’m in the US, and about a year or so ago got my very first shirt with a horizontal lower button hole. I now have three, I think.
I don’t like it. I’ve never had a problem with my lower button coming unbuttoned. I do find it more difficult to unbutton when I want to do so. So I’m with thelabdude that it’s a change for no benefit, and with a downside, however small that downside may be.
I’ve never noticed different colored thread, but haven’t specifically looked. I wouldn’t mind the different colored thread, because that would be a change for no benefit with no particular downside.