Counting cards are useful for teaching place value and number systems in KS2 and 3. This set is made up of a number of cards that represent different powers of 10.
So the smallest cards each have one dot representing units, the next (double the size) card has 10 dots, the one after that has a representation of the 10s cards and so on until you get to the largest card, which represents one million. For some of the larger cards there are meant to be 10,000 spots but I have to admit I didn't check this.
They might be useful to lay out to represent the number 12,045 for instance, but do they have any other use? Well, probably the best use is to help teach subtraction and the difficult concept of "borrowing one".
Pupils can see what is happening as they physically take one from the thousand column and convert it into ten hundreds, for example.
Another (simpler) concept that the cards can aid is addition, with "carrying one" now being given visual representation. The cards can also be used to help with multiplying and dividing by powers of 10, as well as simple adding.
All of these ideas, together with games, can be found as teachers' notes on the really useful free website www.countingcards.com For some pupils at KS23, having to use visual representation may be too simple, but for others, especially those working in small groups, they would probably be useful.