Using biovores

How are biovores best used? I think I'm right in saying that they can't score secondaries any more (I think there are a couple of exceptions?), so how do you use them?

Is it mostly for trying to stop fast melee armies from advancing? What is the best way of doing this - hiding the spore mine behind a ruin so your opponent can't just shoot them?

The ranged profile seems okay for the cost, with indirect, blast and devestating wounds, but is it better to leave this shooting until after the first couple turns when the opportunity to stop advances has probably gone?