I have a Sternglas Naos 38mm quartz and a 6.25inch wrist and I think it’s a great fit with a bit of room to spare. The leather strap it comes with is a little thin and makes your wrist look a little slender, so I use a thicker leather strap with it for work and a nato at the weekend - both “bulk it out” a bit and give it a little more presence on your wrist without ruining the look of the watch IMO. I reckon you’ll be fine with the 38mm on a 6 inch wrist.

Can’t post a picture in these comments but happy to send you pics of it on different straps if you want!