I delayed May-born DS's school entry; he did the summer term in Reception, then went into Y1. I'm doing the same with June-born DD, who "should" have started Reception two weeks ago, but who won't go until next April!
Any difference it has made to DS has been positive. He's now in Y2, and is several light years ahead of his classmates academically (though this is a different problem altogether!!) He seems to have fitted in fine with his classmates, though as there are only 11 of them, that might have helped him to settle more easily.
Overall, I think he benefited from a later start, and I think DD will as well. She still enjoys trotting round helping me, and on the whole, I feel that she gets more out of being at home and spending three mornings at nursery school as she would get out of Reception.
It has helped that we've gone for a private school, as they are more flexible about admissions (in our area, anyway). If they'd gone to the local primary school, there was no option but to start in the September following their fourth birthday, as the place would go to someone else who was prepared to take up the place at the start of the year!