I have had two DSs sit the St Olave's test(s). My elder son is at St O's and we are waiting to find out about the 2nd - he got through the SET and sat the 2nd test. Both also sat the Kent test and scored highly enough to go to the super selectives. They did not sit Bexley, so no experience of that.
From our experience, the St O's maths test is harder than most, with longer questions and requiring more of an understanding of concepts. We did not have a tutor for Maths, but did a range of papers (bond, cgp etc) for practice, along with private school sample papers (often you have to work out the answers yourself as they don't supply them though - I often felt quite "tested" myself!). I have heard that DSs should be scoring over 90% because of the bias towards Maths in the St Olave's test generally (the score on the maths paper determines the outcome for DSs with the same score and there are more Maths questions in the SET than the other sections), but I can't verify that as you don't get the scores. Both my DSs were regularly getting over 90% in practice papers.
For English, we had a tutor for 1 hour a week in year 5, excluding holidays, but did a lot of practice essays and comprehensions ourselves as well over the summer. Luckily both enjoy reading. Because boys tend to have more issues with English, we thought that strengthening their performance in English may give them an edge, whilst also giving them a strong base to work from for whichever school they ended up at. After all, all subjects later on require a good grasp of essay writing and comprehension, so those skills would never be wasted!
For the new SET, we also practiced VR and NVR papers at home from a range of providers - no tutor, but both seemed to have a flair for VR / NVR, so that helped. Being quick is the key with those, so practice and familiarity does help a lot. Practice on these is also needed for Kent and Bexley of course.
Could you share your tutor contact please? I'm looking for an English tutor for my daughter to prepare her for Bexley test.
Also, I have a question about your essay practice - do they need to write an essay for the test?