I played a game this week using a ballistabomb (deepstriking 4x ballistas and an ordinator).
IF you can get in within 18" they are really scary, but it takes your opponent exactly one turn to react to this, and then you are stuck taking pot-shots at 36" because they are sloooooooooooooooooooooooow, and running aint really an option since then you are just wasting away.
Any decent opponent will easily screen you and limit you to bad targets, and with how the new rules for Sylvaneth wyldswoods works, just forget about it.
I would bring 1-2 max, but I don't plan to bring any anytime soon.
Edit: That deepstrike is 540 points btw. So, is it scarier than 4x Fulminators?