I have tried a few different monitoring programs on the netbook I bought for my oldest a few years ago. They worked fine, but the easiest thing was just to tell him that I was going to be monitoring his web use and would take it away if he did anything he shouldn't. Occasionally, I would just boot it up and browse through the history to see what he was doing. He was younger then and porn/girls weren't really an issue. Now he is older and doesn't like the netbook, he says the screen is too small, so he uses my laptop, which has content blocked through work.
Relative to an android based tablet, I got one for my middle son last year. It was about $200, I don't remember the brand, but we sent it back on the day after christmas. It was horribly slow and wouldn't keep the Wi-Fi connection at all. So I can't really help with those except to say that you get what you pay for.