The only difference between 2 and 2b is the accessport dongle. One is a single connector and wire permanently connected.
The other is 2 parts. I believe the only change as because there was more risk to breaking the adapter on version 2.
Outside of that, the functionality is the same.
I bought an AP-sub-003 v2b for my car. It was originally for an 08 wrx but with the latest firmware, it works for an STI as well. Just had to download the AP Manager, take the latest firmware, and download the maps specific to your car.