The class is about under 30 people and particularly in my cryptanalysis class (of about 15 students), 3 of us do maths and others do computer science. Most of the students are international students. For anyone planning to apply, there will be some maths (depending on the modules ofc) but it can be quite heavy (especially if you decide to go more into the cryptography route rather than consulting (people) route. For non-STEMS applications, while I personally think it would be challenge to learn everything, it is not impossible, they do build from the ground up
I highly suggest to read about the latest infosec blogs such as krebs and schneier from now, even if you don't understand it completely. If those articles interest you, then the course is for you! if not, think about why you want to do the course. Another thing which would be helpful (but will be taught, so dont worry!!!) to do over the summer holidays, is to learn linux + how to use terminal, do some CTF challenges, understand how memory works a bit (stack and heap), brush up on your maths (check out modular, groups,...), understand tcp/udp and a bit about how the internet works (routers, dns, packets...). The professors are very kind and helpful and I have yet to find a problem with any of them.
If anyone has any question about the course, do pm me!