Thanks for your insights. Yes, the Edinburgh MSc dissertation makes it attractive over KCL.
Note that Edinburgh has an on-campus MSc of the same name, whereas KCL's on-campus degree is called "MSc Cyber Security", not "MSc Advanced Cyber Security", which is the online version. It may not matter too much since people don't have to write the exact name of their degree on their CV/resume. However, it's something to consider: some universities offer online master's degrees that have no same name equivalent to their on campus master's offerings. This would make it glaringly obvious to employers that it was earned online.
If you are self funding, I would recommend you to consider doing a MBA at Warwick Business School in lieu of the two degrees you mentioned. This is assuming you are not that interested in data science but rather you are seeking to pursue a master's degree to propel your career forward, i.e. for greater income and promotability, especially in leadership positions. The starting salary of Warwick MBA alumni is impressive. It is expensive, as I recall about 43,000 British pounds for the degree, but it would be approximately the same cost as if you pursued an online MSc from Edinburgh + an online MSc from KCL.
As an Warwick alumnus myself, I can tell you Warwick is not an elite school except in the Mathematics Department and Warwick Business School. (For Politics and Economics it's highly regarded internationally, but not quite "elite".) The online Warwick MBA is by far the best online MBA anywhere in the English speaking world. I know online MBAs are sometimes looked down upon compared to on campus MBAs, but that is the case for lower-ranked business schools. Durham has an online MBA too that is well regarded (and much cheaper), but it is not anywhere comparable to Warwick's.
As for KCL's MSc in Financial Analytics, unless you have top grades from your undergraduate degree, it would be difficult to enter the banking, hedge fund or finance sector. They also systematically discriminate against mature students (i.e. if you are past your 20s it's difficult to enter finance, especially if you are seeking entry level positions without any previous relevant experience). An MBA degree is the most "useful" or "fungible" if your main concern is increasing income and general employability across industrial sectors, and if you are not targeting becoming an expert in ML/Data Science. Usually to enter the finance sector one would need to have completed 3 internships at various institutions, and to get your foot in the door for those internships will requires being young (ideally no older than your mid twenties) + top grades from a well regarded school + showing a willingness to work 80+ hours a week + very complaisant and subservient attitude towards the management and showing core malleability (i.e. I am willing to change myself to fit the corporate norms of this company).