I have both and i prefer the tombstone. If you need to recharge your zombies, you can send em on a raid, use the recharge feature and just retreat (if you want a quick health boost). As for the barrel, altho it helps in recharging the zombies, you can just set your ipad/pod/phone to never autolock, and have the zombies rest without closing the app. After 1 hr they should be fully recharged.
So for the healing tombstone, can you just use it by going to an enemy cafe, using the heals before you even click attack for any zombie, and then retreat with no harm done? Or do you have to be inside the cafe before you can use it?
Yes you can use the charges to heal your zombies without having to fight .
Just as advertised, select a cafe to raid. DO NOT SEND ANYONE IN. Click the tombstone, confirm. Wait until the zombies stop flashing/recharging. retreat.
Bingo, +100 energy each zombie.