My 2 cents about this detachment :
- I globally like it (and still hope similar official detachments/formations to come up soon for CSM),
- Daemonic restrictions are too restrictive for me : why would Alpha Legion not use Daemons when they need to ? Even if they were supposed (because nothing may be taken for granted with the Alpha Legion) to fight against Chaos during the Heresy, they could use Chaos to do it. And after 10K years, nothing proves that AL still works as a Legion, and that some warbands of it could not have dedicated themselves to Chaos (or been corrupted by it),
- Nevertheless, I agree to the fact that Daemons would be Allies of Convenience for such a Primary Detachment. Actually, I think that all other detachments/formations should be Allies of Convenience, from Alpha Legion ones (CSM do not trust AL, and even AL must sometimes be wary of ... AL) to Imperium ones (AM/SM/SB/Inquisition could be tricked into working and fighting for AL purposes without being aware of it),
- Stubborn/ATSKNF and Infiltration "for everyone" is a too great (and too easy) buff, IMHO,
- The Warlord change mechanism too specific and aside of the current ruleset (why not just being allowed to keep it unknown under Champion stats until he uses his own stats and abilities, for instance ?),
- The "Preferred Enemy" when AL reveals its agenda is interesting. But I wouldn't make it last during the opponent's next turn (and not making it a double penalty for melee-oriented armies).