hi
i have bought one.
ive been experimenting with it. meaning: strategically using it at times only when i am intensively using my Air, and trying to co-relate its usage with a reduced cycle count.
im varying the maximum charge setting on the Air itself from 80% to 90%, or sometimes setting it at 100% while using the tickle charge function.
so, rather than "needing" to use for battery capacity reasons, im using it to see if i can understand its effect on maintaining overall battery health.
for the MagSafe Battery itself, i really like that its made especially for the Air. fits perfectly and snugly.
as for the charging power that it has, i think it might be able to charge twice - not full Air capacity, i mean twice given my usage pattern of the Air (ie, max. Air charge set at average 85% , and then ending the day with a remaining charge of 40%) with this usage pattern it can probably last me two days without recharging the battery pack itself.
for a very heavy user, i think this battery pack is capable of only about 1 full charge, maybe.
now that there are a lot more cold days here where i live - getting down under 0 ℃ - i haven't noticed the cold adversely affecting the battery, yet.
even though the battery has a slim profile, for Air users, this battery feels very heavy ! so i don't use it when i am out and about, or moving around my home. i tend only to use it when i am doing work at my desk. this is precisely why i can't buy a thicker device as a daily driver. i love the Air for the lightness and "handibility" it gives me.
im not one for buying 3rd party cords, cables, and especially batteries. if i ever need to replace this battery with a new one, i would buy this same one again.