I can't comment on the brand's quality, as I've never used one.
However, note that Fi-Shock is one of the very few companies that still sell some continuous-charge models (as opposed to intermittant, pulsed shock), which are MORE DANGEROUS because they do not give an animal (or person) an opportunity to move away from a paralyzing shock. Make sure that you are not getting one of that type model -- they may (*may*) have occasional application when dealing with extremely-hard-to-confine dogs, and mostly their advantage is that they can be produced more cheaply, but I do not think there is good justification for using one in a backyard setting, esp. where domestic animals and naive people/children may come into contact with them.
Fi-shock does make some intermittant-shock models, I think, if for some reason you are attracted to that company. Read the fine print carefully to make sure what you're getting.
Or, other companies make very small 'garden and backyard' sized units too, of the pulsed-charge type, either battery-op or plug-in.
Good luck, have fun,
Pat