All three of my dses sat the 11+. With ds1, I didn't go for the tutoring, because I felt that if he had to be pushed to get into the grammar school, he'd struggle once he was there. However, when we gave him some past papers about a month before the exam, he did disastrously, and we spent the time until the exam stressing and worrying (though trying not to pass this onto ds1). In the end he passed, but pretty low down the list, got into the school and was happy there.
With ds2 we decided to go for tutoring, to avoid the last minute worries, and he went to his tutor one evening a week for the year leading up to the exam. At the same time his best friend's mum was working with her ds (with family help), basically tutoring him at home - and both boys got in. Ds2 would have got in anyway without the private tutor, I think.
With ds3 we sent him to the same tutor, and after only a few weeks he had a total meltdown about the work and the exam, and asked to stop the tutoring, so we did. He was all set to go to the local comprehensive, but decided at the last moment that he would sit the 11+ (we hadn't withdrawn him from the exam - not sure why), so did it with little or no preparation, and didn't get good enough marks to get into the grammar school. But as we then moved to Scotland, it was moot anyway, and the boys are all now at a very good comprehensive, and I wish that had been the option for all three of them.
The rather longwinded upshot of this is that I agree that it is not a good thing for children to be hothoused - 3 or 4 nights a week for 2 years is definitely overkill, in my book, but a child who is bright enough for the school will probably get in with a bit of extra help either from a tutor or from a parent - there are good practice books and 11+ past papers available.