Trap Wall sections

The way im thinking it could go is to do a "trap wall" you would make a 4 section square upgrade as desired and then enable the trap. When something hits the wall it explodes like a [wall level - 2] bomb.


good things
1 it gives you an "extra" trap (per set)
2 it would be a very nasty surprise during a raid
3 its dual purpose

bad things
1 you would burn 4 wall sections per set doing this (rearming would require rebuilding and retrapping the sections)
2 could be expensive
3 useless against AIR attacks

what do y'all think??