You're welcome, Jeff. I only have the smallest one, and it does the jobs I need done; but I also have a 10mm (3/8") bachi nomi (fish, tail, also at that link as a custom chisel Tasai made me, but it was much cheaper years ago when I ordered it) that's come in very handy, too. In fact, I used it all the time on hidden dovetails before I got the 6mm type 1 chisel.
The only potential problem with the 6mm is that Tasai refused to make me a 6 mm bachi nomi because he had problems making the shank strong enough; so I'd stick with the quality makers, like Ouchi, Koyamaichi, Tasai, and anyone else high quality sold by Iida or Stu Tierney or Hida.
I'd also give LN a try if I were ordering today. Their fishtails are O1 and look real good, about half the price of the Japanese; but the smallest is 3/8".
Pam