In general practice, I get nervous about playing an army that has been jumped on by the power gaming crowd and I've been told Custodes have done really well at 30k tournaments.
This actually makes some sense to me. I suspect custodes could get trounced somewhat easily by about half of the 40k armies. I also think that 30 Custodes would be generally very potent against Space marine legions. (I'm not sure how they'd do against 30k AdMech or 30k Solar Auxillia. I think that 30k Custodes could have an easy time against most 30k armies (on the assumption that space marine legions are the most commonly fielded army).
If I had known the above, I likely would have avoided the army just to avoid the risk. after spending $600 on Forgeworld Tanks, I'm less excited about the idea of giving them up.
This is the most common variation I intent to play.
I'm curious to know what people think of this, both in a 40k and a 30k sense. Note in 40k games, I would still play this with 30k rules and not the 40k rules for Custodes (which I think are a touch more powerful because of Eternal Warrior and storm shields)