This post addresses pruning loppers that are two or three feet long but also applies somewhat to one hand pruners and pole pruners.
The basic rule for using a lopper is: NEVER twist the lopper. If the lopper does not cleanly cut all the way through a branch and sticks, rotate it back and forth around the branch in the plane of the cut to get it unstuck. It is tempting to give it a little twist to snap off the branch or pry it out — resist that temptation. If not you will often chip the cutting blade and ruin it. The cutting blade of a lopper is very narrow and very hard in order to make it cut easily. It is immensely strong in the direction of the cut but quite brittle against side loads, which is what makes twisting or prying so risky.
There are three basic types of loppers. The first is the anvil style that pinches the branch with a sharp cutter against an anvil jaw with a brass or polymer insert to keep from dulling the cutter. The cutter and anvil are usually straight. The main problem is that if you try to cut a green branch of even moderate size it tends to squirt out of the jaws. These also often take a greater amount of effort than other designs.
The second type is a “Bird’s Head” bypass lopper. In these, the curved cutting blade “bypasses” the fixed blade like a pair of scissors. This usually results in lower cutting effort for a given design. But, the curve of the cutting blade matches the curve of the fixed blade. As a result green branches tend to squirt out of this style too.
The third type is a bypass lopper with a cutting blade shape that is more squared off than that of the fixed blade. This captures the branch to be cut, eliminating any possibility of it squirting out. As a bypass lopper it cuts easily and the captured branch is held in an optimum position for the cut. Several manufacturers make these. The Fiskars PowerGear® and Power-Lever® families are good examples of the type.
A major consideration is replacement parts. The part that generally wears out, even with the best of care, is the cutting blade and a worn or chipped cutter is an exercise in frustration. If your lopper has replacements available they will be much cheaper than buying a new lopper. Some manufacturers sell repair parts on their web sites. As an example, a search for “lopper parts” on the Fiskars web site returns various cutter blades for current and past loppers. (It also lists a number of lower cost loppers that are still in production.) Drilling down into likely pictures and descriptions yields model numbers and reference dimensions so you can be sure you are ordering the right part. A replacement cutter is $8 for a $46 lopper and $4 for a $25 lopper, much better than a whole new lopper from the hardware store. Buy a couple while you’re at it.