I bought this for my 5 year old daughter, remembering how much I loved having this read when I was at junior school (I was 8 then).
The book is like the TV show in that it has a unnerving, uncomfortable and slightly sinister undercurrent; the scarecrows are unable to reason, unpredictable and prone to moods and violence. There's no cosy friendship between the two children and Worzel, it's more of an antagonistic relationship from the scarecrow's viewpoint with the bored children just happy to have this secret world of the bogles of which grown-ups are ignorant. You feel however that the kids are not entirely safe in Worzel's company - he's essentially a powerfully built adult with a child's reasoning and a volatile temper. This secret world of the Bogles struck me as more Wicker Man than Stig of the Dump.
It's unlike the TV show in that it's not really a series of standalone episodes, with little adventures being developed and resolved each chapter - usually with some degree of interaction with the general public with humorous consequences. It's more of a serial, and really nothing much happens outside the the world of the scarecrows - there really isn't much conflict, crossover or interaction between the grown-up and scarecrow worlds.
It's still an enjoyable read - sharing themes with Stig and Indian in my Cupboard, and I doubt children would necessarily sense the undertones I've described. But it's not thrill a minute and not cosy.