I may be wrong, but I get the impression (from some posts on endless-sphere) that, although the A123 'nano-phosphate' and other iron phosphate (LiFePO4) types share a similar name & iron cathode chemistry, there are structural differences between them which might result in differing performance (e.g. current supply or 'C' rating) & lifetime: maybe this partly explains the inconclusive trials?
The A123's are not commercially available, as far as I know, except by dissecting powertools etc. batteries.
At 6kg (does that include charger too, perhaps?) the 36V 10Ah LiFePO4 battery weighs more than a 9Ah NiMH? Higher cost, weight & uncertain performance and
lifetime would make it a non-starter for me. A single, taller and higher capacity battery to fit Ezee bikes would be good, but thats a tall order I guess
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Stuart.