Hi, wish I could help more, but tell me what your subject is and I'll try to find out?
I've never met a part-timer in my subject (English), but my gut feeling is that, if you are fairly self-reliant, would only be an advantage for Mst. The full-time course is very short compared with most universities' Masters (9months as opp. to 12), so what you miss out on is time to gather your thoughts rather than time to write or research actively - so having it all more spread out could be great.
The disadvantage is that, in my subject, I came across a lot of rather arrogant, traditionalist faculty members who would automatically disapprove of part-time study and might not give much support.
Anything else I say probably won't be helpful, not knowing what you want to study, but if I can help I'd be glad to do so.
'thestudentroom' forum (google it) is annoying as heck, but might have a few answers too.