Hi hr123, I did my Master part-time while working part-time. I was lucky because I could fit in both things, but it was very tiring. I am doing a PhD full-time now and work only occasionally (e.g. tuitions), and from the point of view of time is much better. Of course you must be able to structure your work and be strict with deadlines. As you said the downside is that you work on your own and feel more isolated. You need to assess which of the two aspects is more imoprtant for you, either the time issue (complete in three-four years), or networking. It is difficult to find the balance. I suppose it dependes on the area you are in and whether you have chances to meet other students through seminars, conferences, etc.