A few weekends ago my husband bit th bullet and Converted to apple, bought two iPads, I also bought lo a leap pad, he is only 2, but it's been fab, he can't understand some of the apps, but he loves it and keeps his attention, which most things don't, so when oh and I are on our doing things and he wants to play, I just tell him to play with his iPad and he loves it, I fairnes he gets much more entertainment from my iPad, but they are paid apps which are more age appropriate. But I couldn't trust him to play alone with our iPads and if he had his own it wouldnt last. Whereas the leap pad is very solid and survived him so far.
The downfalls for me were that apps are expensive for it. At least to me they are expensive. But it's been great for us.
If your child is older and careful then an old iPad may be a better option. Apps are cheaper and can get everything. Any app he has on his leap pad I can get a similar thing on my iPad, most free. Plus you can watch films etc.