Let's make this simple. There are a wide range of zappers from $10 to $1200. In general, even the cheap ones do have some benefit but do not expect a lot from them.
Also, just because it is expensive does not mean that it is good or that it will work for you.
In my over 15 years of experience there are a few tings that make a difference.
To effectively reach far to where parasites
are, you need a good zapper with at least 4 points of contact, 3 points positive and 1 negative / return. A 5th point can be helpful to prevent what they call scattering ( I believe that 4 is enough but the 5th can help insure and provide additional feeling of security ).
Select a zapper that has at least a 30 day money back guarantee and that has a good honest reputation (with their customers).
The zapper does not work as well alone as it does with a protocol. I like the 24 hour water fast, zap, cleanse, and restock approach and have used it successfully.
The have been very few on these forums who have used the good zappers that suggest not using them. Avoid zappers that produce over 11 volts as there is increased risk of neuropathy / nerve damage.
Definitely avoid those that plug into the wall.
The larger the contacts, the better the results in general, so forget the pennies or wrist straps.
Multiple frequencies are definitely better and accuracy is important because accuracy means that your zapper is identical or close to identical to the ones who are getting good results.