Ye, I did
I applied for the Medical School Preparation course and it was great. Not only did I get to stay in Balliol College for two weeks, I met loads of great people (I still message some of them daily) and our teacher was really great! I didn't realised almost everyone was an international student though (this may be different for different groups).
I think the written form part of the application is looked at a lot, because while I have really good GCSEs, so did my friend who applied and while we both got shortlisted I got a place a she didn't, so treat it like a practise for your personal statement.
Hope you get a place, it was an amazing experience and really motivated me to get a place at Oxford to study medicine (have sent off my application!).