If traps make or break a base....
If a trap should define how good a base is then that base isn't note worthy in my book. Although I use the barb testing on the regular... However its hard to barb test for giants once they've pushed into the center of a base and then "boing" a large group of your giants that have packed together are GONE. This troop would be for that purpose. Note the tunnel under wall clause. And to the first responder I agree maybe a little op how i originally posted it.
I completely understand what you're saying
That is why the cost would be exceptionally high for these troops...they would be a rarity of sorts to see during an attack...maybe best uses for Revenge attacks. Cost would go up by 50 DE per level so max level 5 engineer would cost 250 DE. Thats real costly for a troop thats gonna blow its self up or get flung off the map on its on accord or cut the strings to an air trap only to float up up and away with the balloons.