Maybe a little longer with practice. The larger bowls on the Papa-San kiseru are about 7/8ths of an inch across.I'm curious about Kiseru but not a real prospect for one. I do want to ask what the duration of smoking a bowl is. Looks like fifteen or twenty minutes which doesn't seem like time to relax and meditate to me, though as part of a ritual it might be an abbreviated part. If that were all I had, I might become good at it. I have had some prolonged smokes in Group 1 or 2 (smallest) briar pipes using flake cut that lasted much longer than expected.
There is a papa-San kiseru on eBay at a buy it now price of $45, about 25” long and never used. (Free shipping)
I already have two of them, but I don’t see them for sale very often.