I wouldn't necessarily listen to the EA valuations. They're all wildly optimistic round here.
I put in the values for a house we offered on and were rejected. The calculator (and our own analysis of comparable sold house prices) suggests that our offer was about right. Well, according to the Halifax our original, taking the piss offer was probably right. But nationwide think the final offer was closer to the 'right' value. The vendors, however, think their house is worth loads more and their EA isn't suggesting otherwise.
The house we're actually buying has, according to those figures, risen in value compared to when it was last sold (to the building company in a part-exchange). We're paying a lot less than that, and our surveyor valued it accordingly.
So, yeah, not necessarily right (although better than zoopla, which seems to use a random number generator rather than anything likely to predict the current value) but could be helpful in amongst other things.