There’s no reason for a convex or narrow hone to be used on a properly made and honed straight razor.
Glen is correct that other people have tried convex hones. Iwasaki (1960s) even mentions in his chapter for barbers that lapping a stone with loose grit will make it slightly convex and he is correct.
I’ve replied with this image of my glass plate for making convex JNats on these threads on two other forums where people think that no one else has tried one. Crickets every time.
I also disagree that honing on a domed hone is easier. It’s harder to maintain the wear on the toe and heel as even as the center. Here’s Dovo’s own image. Look at where the swarf is on the stone - in the middle. Note that both the toe and heel are off the stone and imagine what stroke contortions you have to do to get even wear on the toe and heel. You can do it, but it is not easier IMHO. On a stone shaped like that you’d have to hone the toe and heel separately to keep the wear even then blend everything together. That’s why many of Dovo’s razors frown, because maintaining even wear on a domed hone is harder, not easier.
Is there a use for them? Sure, they’re functionally a narrow hone as you can see by the swarf pattern Dovo’s image - they’re really only using the middle 1-1/2”. It’s a nice convenience sometimes. I have tringular and pointy (but flat) hones for those cases. But you don’t need a narrow or convex hone.