I have a few MK saffiano bags in blush, and the saffiano just seems like a dirt repellent. I used one for work for 3 months straight, and it only needed a wipedown with a baby wipe every now and then. I wouldn't worry too much about them getting dirty
I love how both sizes look on you. Medium for work and daily use when you're carrying a lot, small for regular use or evenings. Which one did you end up keeping? For the prices you got them for, I'd hope you kept both