So far looking into those has revealed a couple of mayor issues with them;

Only useful for slabs laying slabs flat on something, not any good for ones needing to support themselves, or on their side, as they are prone to collapse! (Suggestion has been to use them along with steel rebar.)

Reports of them rotting in the concrete and turning to mush.

Thanks very much bringing limecrete to my attention, that looks (Yet another!) one to research into.

(For anyone else interested, some info here about it.)
http://www.oldhousestore.co.uk/tech_ohs/limecrete.html

It reminds me in part of Roller Compacted Concrete, I wonder how if it can be made waterproofed ?