Probably the most noticeably different things about St Benet's are going to be that a) there is a monastic presence and b) they only teach a small number of humanities subjects (so if you don't study those subjects don't even worry about being allocated there). Other than that, my thoughts, in no particular order are:
- the male/female ratio will still be a bit unbalanced as they have only been admitting women undergrads since 2016 but they have been accepting women grads since 2014.
- yes, it is a smaller intake (same number of undergrads in total than some colleges have in one year) which some people may find claustrophobic but it does also mean you are likely to make friends across subjects and years and with graduate students whereas a history student at a large college (for example) may mainly end up with friends from their year and subject.
- there are tonnes of opportunities to socialise/network/participate in activities at a university level. Tons. I can't even describe how big the uni freshers fair is but some people manage to barely do anything in their colleges at all.
- you are likely to have some teaching at other colleges plus university lectures.
- St. Benet's will have some student activities despite being small - I know they were pretty good at rowing when I was at Oxford many moons ago.
- the impact of less money is likely to be most felt in whether you have to a private rental in your 2nd year (and, note students at some colleges have to do this too), cost of food and number of grants for travel/books that are available - you would have to look into St Benet's in more detail to see if any of those are affected. It won't affect the standard of your degree and you will have full access to the Bodleian (which renders the need for any college library largely pointless - except for convenience and often longer loan terms).
So, in summary, it is different and it may not be what you imagined from Oxford but it is not worthless and you definitely shouldn't write any of the PPH's off without visiting and speaking to current students.