Experience:
I had a very good experience in Oxford. My academic host was very helpful and welcoming, and I learned a lot from spending time with an expert in my field. The tutorial system means that academics are used to giving hour long one on one tutorials to students, often once a week, so at least during term it is possible to get a lot of feedback if you are slotted into this system.
Though Oxford reeks of privilige and elite institution, getting in is not hard. They are a private research institution, so if you're willing to pay they are generally willing to let you in. Though there might nominally be an application process, this seems to mostly exist in case there are more applicants than there are room for. But expect the price to be hefty. I paid £1200 for one term (2 months), and that included a hot seat desk and library access, nothing else.
While the university is great and staying in Oxford is a wonderful experience in itself, one should not expect to absorb the 'eliteness' simply by osmosis. Rather, one must work hard in order to integrate into the wider research community; graduate students only have precarious affiliation with the university, and research groups are (at least in my experience) more like lecture or seminar series with international scholars giving talks organised long in advance - so the option to present your work does not necessarily present itself. For that reason, it might be a good idea to plan your stay well in advance.