Say:portable media players which feature many amazing functions(Look up incredulous.)
Say:They are tiny and light and easy to carry around.(Look up feasible.)
What do you mean by "sensitive wheels"? (Assume your reader hasn't seen and iPod and that you are introducing it to him.)
Why can't you say introduced instead of primarily introduced?
Say:They weren't popular at all due to the price.A price can't be expensive, but it can be high or low.