I suppose if you need full time, or full days, nursery is probably a better option, but for me, who has always done shifts, CM has always worked out the cheapest option.
I never had a problem with CM being ill, and the CM's I have had have worked their holidays around bank hols, or have taken time off when I am off, or I have taken time off when they are off. As far as I know, its 4 weeks a year. Should be manageable between parents to take the leave?
I get 7 weeks, DP 5 and a bit I think.
I'm not sure how it works if CM is ill. As I say, I've always been really lucky. Although the last CM I had her husband was registered too, so he could have taken over if she was really unwell.