Stefan
if you have finest one i would say it is very close to escher with a lot more cutting power.
I had tested couple different ones and choose 2 which is one huge size and next one is normal size.
Even there is differences between this 2.
To use this stone is a lot easier compare to escher etc ,i mean anyone can use it.Nothing special.
I don't think we all get the same stone.source is different too? i may be wrong.
color of the stones are different.
what i got has yellowish to it but most i have seen in here seems like purplish.
About the lapping.

PA23-250 120 paper will be a little aggressive for this stone. it is soft stone.
if you can start 325 you should be fine.
i usually never go more then 600 and very rare 1k level.
you shouldn't have any trouble to lap this stone.
hope this helps.