There is nothig like integrated mtech at iit bombay for aerospace. its a dual degree.  If you want to really  do higher studies in aero. I would suggest btech at bombay then go abroad.

Btech aerospace at IITK is better then at IITB.

If you are not sure if you should be doing Mtech, then choose btech.  you can opt for dual degree after 3rd year. aslo by choosing btech, if you loose interest  in studyingyou can go after a job sooner.