He doesn't strike me as especially misogynistic TBH, but ignorant and out-of-touch. He conveys a sort of old-school paternalism, portraying girls as vulnerable, potential victims and prey; sweet things we must protect from corruption. There is not the merest whiff of empowerment anywhere.
I haven't read Raising Girls (and won't be buying it) but from the extracts and web-chat, it seems his advice is idealistic, unrealistic and self-contradicting. For example, parents are told to "never snoop" AND to "check her phone" and insist she "has you as a FB friend". They must "keep the lines of communication open" while simultaneously doing several things that would make most DCs refuse to talk to you ever again, like insisting they only use computers in family spaces and removing phones at night.
The articles are pretty lazy bits of journalism (though it's hard to know whether that's the fault of Biddulph or The Mail 
) - they're full of generalisations, pseudo-science and similar nonsense. And it was interesting that he told us repeated in the web chat that he is not an 'expert'. He expanded (22:22): "Remember my role is not to be cutting edge, its to get good information to parents who don't read a lot or have much chance to reflect. Nine specialists in these fields helped shape Raising Girls. I am just the storyteller who makes it accessible."
He's doing several significant things here: he's letting himself off the hook and distancing himself from facts and science (he's "just the story-teller"); he's telling us clearly his theories are reductive and simple (his theories are based on just nine 'specialists', out of the tens of thousands of scientists, social scientists and academics focussed on gender studies); he's making no attempt to keep up-to-date and is comfortable with old messages (he's "not cutting edge"); and lastly, it's his intention to be popularist, not rigorous, let alone intellectual (he's aimed at "parents who don't read a lot")...
So we shouldn't have been surprised (and I admit I was) to find there isn't much evidence to back up his 'testosterone surge' theory: he's not focussed on evidence - he's just telling a story.
You can see why the DM likes him: simple messages, old fashioned, paternalistic... Slightly finger-wagging, but in a benevolent uncle kind of way... 
Those of you who like slightly subtler and more considered theories might enjoy these two thought-provoking short documentaries about Lego (which I stumbled upon accidentally):
www.feministfrequency.com/2012/01/lego-gender-part-1-lego-friends/
www.feministfrequency.com/2012/02/lego-gender-part-2-the-boys-club/
The presenter of these looks forward to a future where girls are "unconstrained by regressive notions of gender"... So do I... And I'm pretty sure this future is not going to be built by Steve Biddulph...