Actually, I think the best situation is a combination of both the Speed Stik and the Power Hitter. Yes, it is a little expensive, but to me it's worth it.
I use the Speed Stik to see what my speed currently is, and therefore check my improvement. The Power Hitter is obviously great to strengthen your 'golf muscles', and learn to swing faster and hit the ball therefore further, as verified by the Swing Stik.
When I first started, my swing speed was 85 mph, whick isn't too bad for a guy 70 years old. But I started swinging the Power Hitter, and have now improved my speed to 90-95 mph (it varies, and I once hit 100!).
And my latest thing is I now use the doughnut AND the Power Hitter, in an attempt to improve even more. My goal is to reach a consistent 100.
And as far as distance improvement - my drives are now in the 200-220 range, whereas they were 180 when I started. My goal here is to get to 250, which I now think is entirely possible!
Swing aids are somewhat expensive, but if you're a golf lover (as I am), it is totally worth it!