What does pIAE do?
pIAE allows you to load most of the over 2800 existing particleIllusion 3.0 emitters in After Effects, including the Pro Emitters. It also includes the emitter search engine that is found in particleView. You have access to all of the "top-level" parameters: size, life, number, velocity, etc. (almost everything that shows in the particleIllusion hierarchy window), so you are able to do quite a bit of customization at both the top emitter level and the individual particle type level (and free emitter type level for super emitters).

What will it NOT do?
Version 1.0 of pIAE doesn't give you access to the "lower level" parameters like particle color gradients, size over life graphs, particle images, particle image reference point location, initial particle angle -- the things that are in the various pages of the emitter properties dialog in pI3. Forces and deflectors are not be present in version 1.0. Also, because of the number of parameters that each emitter adds, there may be some limit to the number of emitters that you can add to a project.

Why would I want to buy particleIllusion 3.0 too?
particleIllusion 3.0 (pI3) is not required to use pIAE, but since pIAE doesn't give you access to all of the settings of an emitter that pI3 does (see "What will it NOT do?" section above), you will need to use pI3 when you want to make changes that you can't in pIAE (color gradients, particle images, initial angle settings, adding particle types, and so on). You'll need to use pI3 to create new emitters, create new libraries, or move emitters between libraries. There will be some cases where you may find that using pI3 is actually faster and more convenient than using pIAE (in complex compositions for instance).

Why Pro-emitters?