I have and they are great. The kids really enjoyed their time and so did I
Not sure if it's the same system but the child isn't allowed to do more than 15 hours a week and there is a limited number of permanent spaces which need to be paid for in advance. So theoretically you should be able to ring and get them in anytime but some are very popular and are hard to get into.
Also they are limited to the number of kids under and over 3. The one that I have C on the waiting list for has only provision for 5 under 3's (which are permanently booked out ATM...) and 15 kids in total being looked after by 2 carers.
You also need to provide their nappies, snack and lunch and a drink.