I haven't used the software myself, but my impression is that Ecodesigner is really a helpful
assess the effects of various early design decisions on the overall energy efficiency of the building.
It won't provide totally misleading data to the client or the project team because that is not what you should use it for.
The figures produced only give you an approximation, and shouldn't be used for calculating anything else. That's why it only costs £200, rather than the multiple 1000's of pounds for fully featured software!
Edit - Sorry, I re-read your first post, and I agree that if you put rubbish in you might get rubbish out, but the architect will normally have an idea of the actual materials right at the start, so 'should' be able to give enough info to make the results of the calculations close enough to still be useful. I would have thought that's the whole point of the program!
Have you looked at the videos on the Graphisoft website yet? (See here
) They might answer some of your questions.