Battery charging stations are not going to damage your Air. The most that a bad charger will do is damage your battery.
The Nitecore intellechargers i4 and i2 have proven to be safe over time with scores of batteries as they must work safely with batteries like IMR/li-ion and Ni-Mh/Ni-Cd battery types and all brands. Charging batteries is their business and there is too much liability for them not to have done it right. If these chargers were unsafe in any way they would be off the market by now. Nitecore sells hundreds of thousands of their chargers.
The charger Arizer is selling has not been through the public use testing gauntlet. The strongest indicator that this is just a very inexpensive charger that Arizer is making serious bank off you — $45 big ones. It is more costly than most of the finest battery chargers on the market while identical looking chargers on the web are selling for under $8 dollars. I know price gouging when I see it. Using an alternative charger to Arizer's is a non-issue if you go with a well known brand.
I am using an inexpensive i4 and I am getting just over 55 minutes on average with my Air. I can't ask for anything better. Also the batteries never even get warm while charging.