So these markets are actually losers from the bookies generally, because they'll typically take bets at decent odds when 'info' leaks which is why they will hurry to shorten them as soon as they see a few bets come in for a particular manager.
For example, Jose Bordalas is currently 20/1 but if some ITK journo claimed he's on our list, you'd immediately get a flurry of bets on those odds which would trigger a liability alarm in the office and he'd quickly go 3/1 or shorter. As we've seen, in the last few days Iraola, Lampard, Toppmoller and Sage have all been favourites at different points.
From a betting perspective, if you know which journalists are reliable and which just talk nonsense (most of them), you could make money if you are quick enough but it's hard because it really doesn't take much to move the odds so it's fastest finger first.
The reason they persist with those markets despite them not being very profitable is that they're quite good for marketing and it gives them things to talk about on social media, blogs and if their PR person gets invited on SSN or Talksport or something to discuss the latest odds.
To reiterate from my earlier posts though, nobody should ever use the bookies as an indicator of knowledge. They know less than us and just react to the bets.