Our trip in 2016, we did not use MBs, even though they were in full swing at the time. For the most part, it was okay. I kept a hold of the actual tickets to scan in for our FPs, etc because I was afraid someone would accidentally drop and lose their ticket otherwise.
BUT, it certainly isn’t as convenient as using a MB. This was particularly the case at Test Track, where you have to scan your MB or ticket in multiple locations. We didn’t know this, and so we weren’t ready to scan our cards just as we were about to board the ride vehicles. As a result, we lost out on one of the fun aspects of the ride. Had everyone had MBs, it would have been no issue at all. (You can still do it without MBs and just the tickets, but it becomes a bit of a juggle.)
So, I’d say, consider the $75 an investment in souvenirs of MBs as well as convenience. For our May off-site trip this year, I’ve made sure everyone has MBs.