I hope this message doesn't reach you too late.
I am currently in Stockholm doing the ICAL LLM. But I found myself in exactly the same situation last summer, I had to make a choice between QMUL and ICAL. Patricia Shaughnessy put me in touch with someone who did the LLM in Stockholm and then went on to do doctoral studies at Queen Mary. That person gave me the following advice (copied email):
"I think your question should be: Do I want to specialize in arbitration? Stockholm's master is about arbitration with a limited number of students. The advantage of this LLM is that it teaches you arbitration only, gives you the opportunity to interact with various professionals in the field and gives you access to competitions. By accepting a limited number of students, you have the chance not only to work in a good size team, but also to build strong relations (The students at Stockholm are selected by the professors. At Queen Mary they are selected by the admissions office). Queen Mary's LLM is more general, although you can specialize in dispute resolution. You must take 3 courses/semester - although the commercial arbitration and investment arbitration runs during the entire LLM. This means that you will have one class/week, compared with 3-4 days/week at Stockholm. The commercial arbitration course has about 100 students, while the investment arbitration around 50 students. You have access to competitions, but this is subject to taking some additional courses. There are also guest lecturers, but not as many as at the Stockholm's LLM. In other words, Stockholm offers you a specialization in arbitration (or an intensive course), while Queen Mary gives you an overview of arbitration and/or dispute resolution.
There are, of course, other factors you should consider: Stockholm vs. London, tuition fees etc. As to you decision whether to go for something more general first, I guess you know your limits and this would be a conscious decision".
I ended up defering QMUL and going to Stockholm. I think I'm going to defer QMUL again (you can do it twice) to keep it as an option.
It's a difficult choice, both programmes are excellent albeit different. I can only say that I'm happy with Stockholm. Good luck and let me know how it goes.