I'm also in Sunderland's MSc in Computer Science with Data Science. I agree that there are lots of reading every week, coupled with mini lectures, activities and discussions. These activities and discussions were indicated as "non-graded" but they require you to include it in your final assignment, I believe it to a certain extent it affects your final assignment grades. So if we take into account of all of that then it is extremely time consuming.
There's no breaks, the deadline of our final assignment is also the start date of our next module. Our current module is even more packed than the introductory one - the new module's first week (this week) has 3 activities, 3 discussions and 1 quiz all within 7 days. The first activity and discussion's due on the 2nd day of class, and requiring a 200+ word-count. From the looks of it, this will be the pace for the next 7 weeks. There is also a major assignment every 3-4 weeks, everything is very fast paced and you can easily find yourself struggling to keep up if you prefer to study on the weekends. I also want to note that I personally find that this is as rigorous as a full time MBA (4 weeks per module, 1 assignment at the end of 4 weeks), so I'm not sure what is the "Part-Time" charm of this course, because you are essentially putting in the same amount of hard work, over a longer period of time per module (8 weeks per module, 1 assignment every 4 weeks)
I feel that the course is structured pretty well that you will be doing a lot of self studying, but yet still learn a lot, perhaps more than attending a lecture in university. & That's a plus for me. The assignments don't really leave you thinking "why" you did them, but you definitely walked away with a ton more knowledge on CS.
One thing that puzzles me though, for our first module, was that our tutor was a Bachelors' Graduate (recently in 2018/2019) who will be grading both assignments. I'm not sure if that's a thing for online studies, but it was just something that seemed strange to me (I was used to being graded by professors). Our tutor was very responsive though, even being available outside of school hours.
A final thing would be with that with online learning, time zone might be an issue for students, and Sunderland has a weird schedule in general (first classes starting on Tuesdays instead of Mondays), so deadlines would be in this format too. You are required to have discussions by a certain deadline, which usually fall between Wednesday to Friday EOD (UK Time). For me that would be one of the biggest concerns with regards to class participation. I'm working in a different time zone and have a high workload in general on weekdays, the level of participation needed throughout the week (activities & discussions) are a little too excessive for me - since they require the inputs before Friday EOD of each week. You are essentially forced to take time out of your long work day, or if you have children, you can expect to stay up past midnight instead of given the option to sacrifice your weekends.
I hope this write-up is useful in helping you decide - I'm sure the course is better than the one offered than York (based on the horror stories I've read), York also has terrible support for their online MSc (I applied to York and a few others before ultimately choosing Sunderland).
FWIW, I will definitely stay in this course unless it makes me think otherwise. For anyone curious, we'll be having a hands-on course in Software Engineering coming up in May, will probably update more then!