I bought this to replace the old CD I had lost. I'm glad it was lost now, because this is a much better product. There are definitely much more definitive CDs to be had, but the thorough way this one covers the 40 species included is very good. First Geoff Sample gives a brief interpretation of what you are about to hear and then the clearly recorded bird songs and calls follow. The author highlights any similarities between the species, such as with the tits and he groups similar birds together.
If you're not an expert and you're looking for a product that covers pretty much all the birds you're likely to hear in your garden, at the local lake, or down the wood, then I would strongly recommend this CD. As for me, it was worth buying just to see the look of confusion on the cats face as she tried to stalk my speakers.