@inneedofwine If there is someone at your school who passes these exams this year, then I suggest that you approach the relevant parents and ask them which tutor they used. I wouldn't ask whether they used a tutor, as you may not get a direct answer, but whenever I have asked this question (ie who) of someone who has passed, I have always been given a name and phone number, and I have yet to meet the boy who did not have some preparation. Primary schools approach the curriculum in different ways, and at different times, so it can be helpful to go to a tutor who knows more about your current school, and where the gaps are likely to be. I would expect most tutors in the area to be familiar with the standards required for these exams, as well as for the grammar schools.
In terms of the question of whether tutoring is a good idea or not, I think that exam preparation is essential, and actually a very good skill for the boys to learn at this age. Boys in the top 5% of the ability range would probably pass the independent school exams without much extra preparation, but as the schools offer generous scholarships which are financially valuable, even these boys end up doing additional preparation. And to be honest, if a family is not willing to prepare for the exams, then potentially these schools are not the right destination for you. But tutoring comes in many shapes and forms, and it is important that your son is comfortable with the level of preparation required. For some families preparation with one or both parents is sufficient using resources such as the bond books and ISEB papers. For other families that is not a good option ( due to time, personality or confidence) and an hour a week with a tutor, together with an hours homework for about a year ahead of the exams seems to be about the average. But a tutor per se is not strictly necessary, though I would suggest some preparation is.
[Sorry, small rant as it frustrates me to see bright boys either not try out for these schools as they don't realise the potential fee remission available, or that they're told not to bother with tutoring and equate this to not even looking at Bond papers].