They do look good on paper but I have heard from several that the nanotech series' ratings are wildly over the truth. I think Gary used them last year in his feather and was disappointed. I have used the regular Turnigy packs (second hand!) but having never had them in a high power bot can't really comment on their performance. I can say confidently that they are batteries.

The packs from Component-shop seem to be quite good, and although pricey Optipower are the real deal. You can get a roboteer's discount to soften the blow with them.