Better: More ID Codes
ALPHA has 100 ID CODES. Astro has 50 ID CODES.
The ID CODE is what differentiates one Garmin ALPHA collar from the next, so you can run many Alphas in the same area without interference.
If you are only running 5 dogs, instead of only having 50 codes, now you've got 100 codes which should really eliminate interference for the guys that aren't running that many dogs.
For the 99% of the folks, increasing the number of ID CODES and eliminating more chances for interference is a great feature. 50 extra codes will help guys running a huge number of dogs, but it's not going to completely eliminate interference.
Garmin also changed the way they are numbering ID CODES. The Astro is numbered 1-50. The ALPHA has five numbered sets, and then each number has 20 subsets. 1-0, 1-1, 1-2, 1-3 and it goes all the way up to a 5-17, 5-18, and 5-19.
This is designed to keep folks from thinking that you can track and Astro and an ALPHA at the same time (which you cannot).