Rootbound only means your plant will be stunted in size, which can be an advantage if stealth & space are issues. If you don't mind watering often & dealing with nutrient issues, it's not a problem at all. It requires more time & attention than growing in a bigger container but is totally doable. There are folks who grow in much smaller containers (check out "Stunted's" work. He grows in tiny pots that are almost the size of a thimble). He has to wake up in the night to water, but if you've got the time...and OCD...it's a worthwhile hobby I guess.
I'm growing an auto in an 18 oz. Solo cup now. And I do have OCD by the way. It's not for the careless or busy, that's for sure.