I think at 5/6 years old you should perhaps use all the different free sites available and vary the options that your child practices on.
If you type in KS1 maths a lot of many different sites will come up and many are fantastic,
We have used Mathletic, Whizz and Education City, all of which have been excellent programmes.
Education City is cheapest but offers a great variety for young children. My children got a lot out of this
We moved on to Whizz and I am a great fan of this programme, but it is far too expensive for a Year 1 child. They need to be using the programme for about 60-90 minutes a week to really benefit from it. If they dont, they soon forget how to do the strategies and they will probably move much further on that what they cover at school. For teaching, this is definitely an excellent package.
With Whizz you dont have any control over what your child is learning, so it is sometimes not in sync with what they do at school. The good thing is it covers the entire curriculum and the child cant choose not to do a topic because they dont like it.
We now also use Mathletics (should say we have registered) and this is a good revision package but it is lousy at teaching strategies and new concepts. Your child can select what they want to learn and ignore what they think might be too hard.
There is a lot of excellent stuff on mathletics and it is good to use in tandem with other learning opportunities.
All three packages are very different and not comparable.
I only mention these because this is where my knowledge is.
I also recommend the Jump Ahead computer series, they are excellent.