Better to use Ambush from Map device at 4c or used Rusted Scarabs at 9c a pop ?

Is there a material difference between using the map device ambush option, which only costs 4c a time or using a scarab, which even the base ones are 9 chaos a pop. Do they both give the same rewards or is the scarab a better deal even though it's twice as much in terms of chaos orbs ?

The idea is that you can use them together.

True - you get 7 strongboxes that way but individually the scarab gives you less strongboxes then the map device does. As long as I have the funds I guess I'll go with both !