I have the out of production FX3 model that is still running strong. I don't think you can go wrong with any of their models. I upgraded mine to use re-chargeable batteries.

As stated above you can't call in coyotes that are not there.

A tactic that I use is to drive my planned hunting areas early in the morning before light and stop and run my coyote challenge call. If I hear a response I will take some flagging tape and tie it off on a limb by the road. I will then drive about a 1/3 mile and do it again. I will attempt to find 3 places where I got a response and then go back to those areas to call. I have been much more successful using this method than calling blind.