The best stubble trimmer should be able to trim your stubble to a number of different lengths and should have durable, self-sharpening blades. It may also be best to look for a stubble trimmer with flexible guides. You should also choose a trimmer with a good charge time and long battery life, and the trimmer itself should come with a reasonably long manufacturer's guarantee.
A good stubble trimmer should be able to trim stubble to various lengths. Some claim to be able to go up to 0.01 inches (about 0.5 mm). Lengths generally vary between this and 0.7 inches (about 18 mm), so choose a trimmer that will give you the length range you prefer. Some trimmers have limited length ranges, from 0.01 inches (about 0.4 mm) to 0.19 inches (about 5 mm), for example, while others offer more flexibility. Some trimmers have motorized length control, which means that you can to adjust the guides with a push of a button. This feature may be helpful if you want precision trimming without having to adjust the guides manually.
The blades of the stubble trimmer should be durable and should also be self-sharpening. Stubble trimmers with self-sharpening blades generally require no blade maintenance and do not need to be oiled. The sharper the blades, the more effective the trimmer will be on coarse or thick stubble.
A stubble trimmer that features flexible guides follows the contours of your face a little more closely than those without. This may help to trim the stubble to an even length, even in hard-to-reach places. Some trimmers feature floating contouring heads, which may also help to give an even trim. It may also save you from having to hold the trimmer at uncomfortable angles to get an even trim.
The charge time of the trimmer is another important consideration, especially if you cannot leave the trimmer charging for extended periods of time. Some trimmers can be used after having been charged for just an hour while others may require much longer charging times. A trimmer that can be used while it's on charge may be a better option if you have a busy schedule and can't wait for the trimmer to charge fully before use.
It's also best to look for a trimmer with a lithium ion battery as these batteries are believed to be both durable and powerful. The battery life may vary from one model to another along with the usage you'll get out of one charge. Some models offer up to 50 minutes usage on just an hour's charge, and this might be a good feature to look for if you travel or if you need the battery to last longer between charges.
Before you buy a specific stubble trimmer, you should always check whether the manufacturer offers a guarantee on the product. Most trimmers will have a guarantee of some kind, but the length will vary depending on the product and manufacturer. Some manufacturers offer guarantees of up to three years, and the longer the guarantee, the more peace of mind you'll have.