I think it is better to just come up with your own content. Most of those type of programs that are designed to make things easier, really just make things more difficult. You are right. The more you write, the more practice you get, and the better you’ll become. I have been writing for years myself, and I have never needed any content generation programs.

Google is getting VERY good at catching spun content so you'd better be talented at manual spins. If they DO catch you, of course they'll spank you... and hard. So anything you use spun content on is inherently AT RISK. Worse yet... Google gets better at finding spun/poor content every year. So in the longrun you're screwed. I'd weight your other options and see if you couldn't find a cheaper source for manually hand written content.
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He saw a trainer nearby and asked why these animals just stood there and made no attempt to get away. “Well,” trainer said, “when they are very young and much smaller we use the same size rope to tie them and, at that age, it’s enough to hold them. As they grow up, they are conditioned to believe they cannot break away. They believe the rope can still hold them, so they never try to break free.”