I'll go one step further to say that ground plane wires and the booster are not mutually exclusive. Each addresses the signal issues in a different way.
To really know if your layout requires the booster, you should build a signal strength test car, and measure signal levels around the layout. Technically, you should only employ the booster after you've exhausted the possibilities with ground plane wiring. If you haven't done that, the booster alone may not solve your problems. Further, not all signal problems are the fault of the layout. Some may be caused by factors unique to the locomotives themselves
Having said all that, I don't want to discourage anyone from purchasing one. At worst, it's a $20 donation to the American Cancer Society in Dale's name. At best it might be a magic bullet for you.
I have one of Dale's prototypes on my layout right now, and while signal strength has greatly improved layout wide, I still have problems with some engines, leading me to believe that the trouble can be internal to specific engines, things like antenna placement and length or shielding of a coil on the rail sounds board on earlier TMCC engines.
