The advantages are:
it does all the things what we want
it brings groceries
it mails letters
it tends the lawn
it will arrrange  and clean the house
the disadvantages are
it can harm humans 
it might not work and behave differently
it can throw things in dustbin which are lying on floor
1 4 1
brother disadvantages 3rd point is in correct its an advantage
ultrab means that any useful thing on floor may be treated as a useless waste.