It doesn't take into consideration the troop type, only the amount you can loot with the troops you select.Each upgrade takes longer to scavenge, but it brings a lot more of each res, making it good for start up or for people who don't have the time to farm constantly.
Farming is still better if you are active enough(or will be in a few days).This is a nice tool, but I can only see it working for the first week of a world or in a very competitive area.Scavenging is something you should use for no hauls worlds if you really want it to have an impact on people's growth up until mid game.It's a nice new feature though and that premium option is not worth using so I doubt a lot of people will use it.One of the first features that can be boosted with premium that isn't unfair for players who don't pay to play.
Good job, inno.