First I bought a Parazapper CE, this worked great with a fresh battery but that dropped off too quickly.
Then I heard about the Ultimate Zapper and saw the 3 month trial offer and ordered it. Now using it for about a week and this is the one that works best for me.
The penetrating power of the UZ is just what I needed.
But make sure you order the footpads, I am using the ones I got with the Parazapper.