I must admit, I don't think the Brits' guide is great (I've had mine for a couple of weeks). But I think there are a couple of reasons behind this - one, I've done so much online research that it doesn't feel like it's telling me anything new, and two, before we decided to go to DLRP this year and leave WDW for when DD is older, I was given The Unofficial Guide to WDW With Kids, which is fantastic. Brits' guide seems a disappointment after that - the Unofficial Guide is so incredibly detailed and has lots and lots of general tips.
I wouldn't say there's anything WRONG with the Brits' Guide though, and where it has been useful is in allowing me to methodically go through the attractions one by one, and figure out what we're interested in (and what DD is too little for), without having to struggle through the DLRP website.