Imp is a lot worse than it could be, because you can only use one at a time.

I was thinking about the options available to cloakbot... and realized that I basically never want to use the imp. If I was planning to use crawling bombs then I would get the roach or something else.

It's not that the imp is terrible *by itself*... It's that imps can not chain explode: the first imp stuns the others.

That, and using the imp with a cloaker is very hazardous to the cloaker, It's pretty sure I've seen more friendly cloakers stunned by imp than enemy units. By comparison, the roach's smaller blast range makes it easier to use.

Sure, you could use the imp one at a time, but that is a ton of micro.

It would probably help if it was more like limpet where it does not friendly fire, but on the other hand would it upset the game balance?

imp can achieve things you can't with roach. A good example is countering shieldball that has outlaw: roach will die too far to do significant damage, while imp will effectively stun the outlaw and subsequent imps will stun the whole ball at the end.
Also imp will be more effective at stopping a ball of ravager rather than snitch, cost wise.
But yea, need micro.

If you press D then all the selected Imps explode.