I used to do them for a different company.
Actually kept going for a few months...you get paid by the plasma company for each visit (besides the MS job money), and just as in donating blood, you get your blood pressure, pulse and hematocrit taken each time, so that's a bonus. Every couple of months you have to have a fuller medical evaluation, so again, a bonus health check. Towards the end I was picked for a Rabies Immune Globulin special group, so I actually got some pretty expensive vaccinations on the Plasma company's dime. But after a while my veins didn't appreciate being poked so often in the same spots, so I ended that.