Each of the battle engines have a different role to play so will be in different lists depending on the faction.
I think they are all 9 points apart from the Retribution's gun platform which is 10.
Asking if they are worth the points is difficult. Lets take my main faction, Cryx. The wraith engine is 9 points of infantry slaughter. Each time it kills a living model it gets a soul and can use that like a focus point boosting or buying extra attacks. It's got Dark Shroud to give an armour debuff, which spreads out 2" from its 5" base affecting a large amount of the battefield. And it can go incorporeal every other turn to protect from damage and reach places other things can't.
In the minus column is the fact you can't hide it, at all. It's easy to hit and damage and thus will die to a stiff breeze. Thus it will take a while for people to learn how to use it. Some battle engines have an obvious use and thus will be seen more often, the Protectorate and Khador ones for example will cause major problems for the enemy infantry with their pushing flames and rough terrain causing guns.
Muse on Minis did an interesting write up on getting a battle engine in a khador list. Using it to increase the effectiveness of the warcaster without taking their resources (focus). I haven't found that sweet spot for Cryx yet but I will keep on trying.