As a seller of zappers, I feel that if all that you can afford is a cheap zapper, then the z4ex can be an all-right choice.
The issues are basically a question of accuracy that some feel is not important.
Having been involved for 15 years, I feel that it is very important.
Here is a video about a zapper that is as almost accurate as a Rife machine, produces 14 frequencies instead of 3, and is reasonably cheap, only a few dollars more.