Of course it's ok! It also depends what you class as affordable- just affordable or easily affordable. We are lucky and also have worked very hard to give us a choice of using independent schools, however we aren't rolling in cash and In order to afford both of our children we would have to both continue working and prioritise spending. I suspect we are like many others who could afford but it would mean compromise. We haven't at primary level as our local village school is excellent.
We did accept an independent school place for our daughter at secondary level and paid a deposit but in the end she wanted to go the state school she was offered as she felt it suited her better. It would seem grossly unfair for her to have to go to an independent school just because we can afford it and to make sure we don't take a place someone else might want!