I think It's up to person. As for me, I would use 니다/ 요/ .. But, most Korean also would think someone who don't use 니다./요 as rude or impolite. So, I think if you met someone who don't use 니다/ 요 from the first time you meet, just ignore them. because they must not have gotten good education. Lol.. and also It would be very hard to understand all things they said because even Korean like me, sometimes I couldn't understand whole things that they said.