The good thing is that once fully mastered training is much cheaper than it use to be, but it is rather useless in the begining. I tried the skill on Dead's man lake in a 1on1 vs a computer player.
The result was pretty dissapointing. I started with Dougal, as he has the quickest developement and I played rather ok I would say, with no big losses and good creeping. Found Ellaine in the tavern so I might say I was lucky. Furthermore I found the bow of the unicorn on a skeleton, which was a strike of gold...
The problem was that usually by week 4 I would have already upgrade some peasants into archers that way significantly increasing my army. And since a knight's only power is his army I was pretty weak. I trained some archers in the new training limit but 7 per week is hardly enough.
The other trouble I had was that in order to train a unit up the tier you need to have built the dwelling of the upper level unit. I mean for example if you want to train priests into cavaliers you need to have the cavalier building, and that is very expensive resource wize. In order to make this effective you need to build the training house, the Hall of heroes, get all the skills required(Exp Counterstrike, Expert Trainer) and build all the dwellings which can hardly be done early on due to the high costs.
The result... see for yourself:

Jezebeth... leading a large inferno army came attacking in week 4 day 1. She stopped just near my town so I could not go in and I had to attack. Her skills consisted in a mass slow, expert gating and a 110 damage eldrich arrow.
My army just stood there while the familiars and hell chargers were hacking away...
I tried the battle quite a few times, and the closest I came to beating her was one time when I sold all I had to buy creatures, but still she had 2 pitfiends left when I died.
Anyway... this first test prooved to me that right now haven is pretty weak early on, especially due to the high resource cost of dwellings(ore especially) and to the fact that their hero is not that strong at low levels.