I wouldn't say that the "Air Link" style backup reg is any better than having a properly secured octo. I would say it's simply different. Regardless of which reg setup is used, the problem that divers encounter is that they don't practice sharing air often enough...so when they encounter a stressful situation and need to share air, the procedure doesn't unfold very smoothly.
If you have a leaky power inflater button, then the standard procedure is to disconnect the LP inflater hose. If you do this, you won't have access to your backup "Air Link" style alternative air source. Admittedly, if you maintain your gear properly, this should be a very rare occurrence. Even then, if you needed to share air, you could still buddy breathe on the primary reg with the OOA diver.
Personally, I like keeping my backup reg separate from my power inflater/BCD exhaust buttons. In my experience, this simplifies things while doing a shared air-ascent. If you end up going with an "Air Link" style backup, make sure that you practice using it during shared air-ascents.
I prefer to dive with two identical, high performance second stages. This simplifies servicing and maintenance. Moreover, on a dive trip, I can carry one backup overhaul kit that can be used with either second stage.
FYI, I am strictly a recreational diver. I dive with my primary reg on 5 ft. hose and necklaced backup reg on a short hose (24 in. long). In an OOA situation, I would donate my primary reg and breathe off of my backup.