Octo-ooze at level 5 may still seem weak, but with the size-10 Housing space, they can easily overwhelm Snipers, Bunkers, Teslas, even Drull if used in large numbers. It is recommended that you upgrade them to level 5 before facing Lasers and Cannons. At higher levels, Octo-ooze can still be efficent, and can be used to take down exposed Aerial Defese Towers. And Octo-ooze can also be used to farm the Kozu tribe with the help of Fomor and Zafreeti.
Octo-ooze can be efficent in bunkers, being able to stall the PPX tatic.