Poland 1-0 is +750 and Poland 2-0 is +1200. Those are 'near top-end' prices which would be a net +414. If you like those outcomes then +450 would be a very fair price. Poland win & Under 3.5 would include Poland 2-1, (+950), and 3-0, (+2200). That would be a net +200 so +230 would be a very fair price.
I make no comment as to a recommendation of the book you mentioned.