Stuart I think it's quite acceptable. I'm not fan of the opaque style photo boxes because you don't have control of the light very well. I would take the same PVC frames that you have and cover them with translucent white fabric. Then you can shine the light through the side, the top, or even the side and top to create a different look to the piece.
My only feeling about the photo you have is that it is good for that piece. However the inside is a little dark which is not bad for that bowl but if you had important detail on the inside that you want us to see then the translucent photo booth makes it easier.