These mole stakes are absolutely worthless and definitely not worth the $30+ price tag not to mention the extra $10 you'll waste in batteries that you can't return. They claim to drive away moles and gophers within 14 days of installation. I gave them 21 days before completely giving up and returning them. If anything, the mole activity increased after installing the sonic spikes.
I have a semi-wooded ½ acre lot and end up doing battle with the moles every year, but they have been the absolute worst in 2008! I figured I'd try the sonic spikes this year as I have a friend who swears by them. Unfortunately that wasn't my experience and after reading several reviews of similar products, the Sweeney's Mole and Gopher Spikes appear to be equally as worthless as all of the other brands.
I'm going back to my old standby, Juicy Fruit Gum. Follow the mole run and make a small hole every 10 feet or so. Drop in a fresh stick and cover the hole. The next time the little bugger goes down his run, he'll eat the gum and die because he can't digest it. It's much cheaper than sonic spikes and pesticides, less of a pain than traps, and has been the most effective thing for me at significantly decreasing the mole activity.