Gas-powered trimmers tend to be more powerful than electric trimmers, but they are louder and need to be refueled regularly. Corded electric trimmers are just as powerful as gas-powered trimmers but the hassle of using an extension cord can be annoying for some. Battery-powered electric trimmers allow for the freedom of gas-powered trimmers, but they typically are far less powerful.
Some hedge trimmers have a kill switch installed, making it impossible to use unless both hands are on the handle. This cuts down on the chance of injury, but holding down the switch non-stop can be tiring. Alternately, there are trimmers that have no safety switch, but these can increase the chance of injury.
There are many factors to consider when it comes to a hedge trimmer's blade. A shorter blade is easier to control but obviously has limited uses. Some trimmers use double-sided blades, which make sculpting and multi-directional cuts possible. Blades can vary in the length of the gaps between blade teeth and in the material used to build them. The closer the teeth are, the more powerful the trimmer, and blades made with high carbon steel stay sharp longer.