NPK analysis isn't the whole story - most of the nitrogen in dried chicken manure is in the form of organic compounds and is therefore slow release (more than a year before all of it is made available by the action of soil organisms.)
In practice, this means it should be regarded as more of a balanced fertiliser than the figures suggest.
Price-wise, it's currently being sold in Wilco for £5 for 7 kg, which I would think is cheap compared to most high street/GC prices for Growmore.
Against that is its lower overall NPK content, in favour (for some) is that it's a natural, sustainable product.
As for what works best for which crops, most of us can only try to guess what nutrients our soil may or may not be lacking and therefore whether a specialist fertiliser is or isn't required.
Each to their own - I mainly use dried chicken manure and some Growmore, and also a liquid feed if I think a quick fix is needed for leafy crops (most general purpose liquid feeds are high in nitrogen.)