For finishing the glass both inside and out Scrim is better than a MF all day long. Loads more resilient too.
The other problem we had with MF's was that they grip onto everything (grit, dirt, wood shavings, sawdust all become part of the MF. Magic sponges seem to be at war with MF's and could often be found dissolved at the centre of a MF after inadvertantly getting in the wash, never to be parted again).
In short MF's soon become useless as they get all sorts stuck to them that washing can't always sort. We tried several types, including Unger (best for quality but pricy for size), and they would be fine for less mucky work so general WC should be OK, but I would still favour a scrim.
I have scrims that have been going strong for five years that still work a treat, look a bit tatty and have thinned but still do the job. Bear in mind this is for builders cleans so everyday WC shouldn't ever be a problem.
We do wash scrims on there own to help prevent them getting fluffed from other rags.