Hehe, you realize the hole has to be big enough to bury a cement vault that is 35"x35"x92" with 18" of dirt on top. You are talking a hole minimum 110" deep and 36" diameter...really you would need about 40" diameter to give enough wiggle room to get the vault in. Oh and this hole could have to be dug in anything from clay to limestone.
But I wish I had one of those machines when I built my 5 room addition. Hand dug and poured 19 cement piers.