Used housenetwork, loved them too. Do a mumsnet search on 'house network' and you will find hundreds of positive posts about them (it's how I decided to use them). The only dissenting voices are the traditional estate agents...
I usually say that the only time I wouldn't recommend them would be if you were selling a house to a demographic who doesn't use the internet (i.e. selling a pensioner bungalow). Otherwise it's a no-brainer.
However, you say in your original post "I really want him to have minimal stress in moving house if at all possible. A good estate agent would help!".
If stress-free is more important than money-saving, then I think this would be the one other occasion where I wouldn't necessarily recommend them.
You do have to do all of the work yourself (the valuation, re-write the copy, select the photos, do the viewings etc), which is fine if you are market-savvy, as you can do all these better than any estate agent anyway. Housenetwork frequently attracts sellers who are like this, which is why so many, like OneStep above sell really quickly (we sold within 2 weeks).
But if you want it to be as stress-free as possible, your DF would be better off going to a traditional agent, who does all the leg-work for you (for a [hefty] fee).