The way I see it, it's better to go for a shiv primarily because of the increased range over the atomizer. But I know that for other gear (swords/guns), you don't want to go from 4 to 5* unless you have the radiants to get them up to L7 or 8. So does this apply to AoE bombs as well?
http://forums.spiralknights.com/en/node/94450#comment-845250
This was on page 2.
Shame on you.