an externally balanced kit can also be balanced or unbalanced from the factory. So yes externally balanced and purchase prebalanced with the rods pistons crank flexplate and balancer. These kit will usally turn 6K but if the engine is going to live at 6K its not as good as internally balanced.
The pre balanced kits on an external blanaced engine are as good as the oem do when they slap them together. that being said the factory was not building a 6K rpm engine. I have seen them work just fine being slapped together. I have also seen them go to the machine shop and need lots of work to get right. factory balanced usally just means they weight the kit parts and make sure they are all with in the spec for a balanced kit. not sure about eagles process they say alot of fluff on the site but it doesnt seem to be the case when the kit lands on your door step. That being said dont buy the none balanced kit because guess where all the parts that were out of spec went... One piston too light and your F'ed. Every piston will have to be modified to make up for the difference then the crank shaved to make up for the lighter pistons. yada yada yada...
Internally balanced is good but the cost is alot more initial and more time at the machine shop. But if your going for full race motor you will need it for 6500 or 7K rpm engine.