For grow out beds I would use the 1/4 - 3/8", the smaller one would be for pots. In my opinion, 1/4"+ is too big for shohin trees or trees that require more water.
I checked them as well, still too expensive. Their 3 gallon is close, still $3 more. But their 6 gallon at $64 shipped is still almost $30 more than the 1 cubic foot, and 6 gallons is .8 cubic foot, so you get less pumice as well.
I ordered a pallet from general pumice, it worked out to $18 a bag, including shipping. I got both 1/8 and 1/4 inch, it is very clean and size consistent. Lexie is awesome to deal with.
Definitely going to have to check them up. Last time I checked their site they were slightly higher. I can't open their site here, I guess they are probably running an outdated SSL.