If you're looking for a guide to take out for a walk with the kids, then this is a good choice. If you're looking to buy a woodland, then you'll be disappointed.
The guide identifies most common UK species of tree, but doesn't go into huge detail on the subtleties of exotics and sub-species. This may or may not be a problem for you.
The style is of cute watercolour illustrations for each species; their overall appearance and leaves, together with a good listing of similar and potentially confusing species. I wasn't over-keen on the use of illustrations as a species guide, rather than photographs. They work quite well for the leaf close-ups, but the overall outlines are much less clear. This makes the guide hard to use for identifying silhouettes on adjoining hillsides.
It's a good enough guide for starters, but on the whole I'd suggest some of Collins' other field guides instead. I particularly liked, "Collins Wildlife Trust Guide: Trees of Britain and Europe", mainly because of its good photographs.