It tends to be harder to stick with things that feel "optional," especially when they compete with necessities like holding your job. Thus, the biggest downside to this would be if you do not have the time or energy to pursue the Master's program and this results in poor marks.
If you apply for other degrees and/or visas, you may still have to declare that attendance and coursework, possibly with transcripts. (See Can I omit my undergraduate school from my CV? and Can I legally omit the fact I hold a Ph.D. degree?) You could certainly explain the circumstances when you're forced to mention it, but ideally you don't have to explain anything away to begin with.
You could avert this problem in several ways, such as officially withdrawing from a course instead of failing it (if possible in that system) or making sure to devote your full energy to each course you take.
Given your purposes for taking the class (interest and extending your knowledge), would it make more sense to seek out an open online course instead, or an interest group local to you?
This is a warning about a factor you may not have considered, and I don't mean it to sound needlessly harsh. You could learn great things from this program. Successfully completing this degree will probably be neutral-to-beneficial when anyone reads your resume/CV, and what you learn and practice there may be adequate proof of the program's success. Further, if the program later becomes accredited, your degree will accordingly gain in prestige.
