It's not auto at least from the way I'm reading it.
Seems to me like you have to actively select your targets to cast the lightning bolts and furthermore SLAs take only six seconds to activate. Now, considering a typical round in D&D is about 6 seconds. Six second lightning bolt SLA , six second selective fire lightning bolt, seems kind of redundant to me.
Don't get me wrong I'm not saying its a bad spell. We just need a little something more to it for it to serve a use.