total tangent now, but since you brought it up...

people are really liking the whole 58.4mm tamper piston thing? i was thinking about ordering a new rb tamper anyway, i could certainly have him make it this size. it just seems odd to me that you wouldnt want some coffee to push over the sides of the tamper...

I have one of the Cafelat VST-sized tampers.

I don't think it make a difference at all, except for the fact that it's flat. I'd rather use a 58.0mm convex than a 58.400000000000000 flat tamper.

I was reading something somewhere a couple of days ago regarding using a 53mm tamper in a 58mm basket. Apparently it works just fine.

Tampers and tamping are 95% voodoo and marketing IMO.