I graduated two years ago, it took me 6 years of part time study to get my BA alongside 3 children, a full time job and a divorce.
Could not have been prouder of myself and I'm not doing an MA - was going to continue with the OU for this too but ended up finding the course I wanted in a local university.
I would really encourage going to the face to face tutorials if you can, I found they really helped.
You do have to be motivated which is why it's worth choosing a subject that you're interested in.
As far as helping to get a job goes, I know that others are correct in saying it's not relevant for all careers, but as far as my employer was concerned, the dedication and commitment into gaining my degree was a real plus point for her in giving me my job.
The Facebook group for the course you decide on can be really supportive (although a lot of competitive "I left my essay until an hour before" and "I've got 25 children and I'm still managing") but it's great for asking little questions or for reassurance that you're not alone! They also tend to have separate groups to share marks which means you don't have to feel rubbish if you haven't done well and worry about people sharing.
I would also say that tutors are a lucky dip. I was really lucky with mine and had one who would respond to emails and phone calls within hours, but I do know others who would ignore and not mark essays until well after the deadline.
But I highly recommend doing it!