This design is more convenient than having to change combs all the time, but many adjustable guides are flimsy, and most do not offer enough range for thick, long beards. Many trimmers, especially inexpensive models, have a single, adjustable-length guide comb. Rigid, fixed-length guide combs: Earlier versions of this guide favored trimmers with multiple, fixed-length guide combs, which determine how much beard is left after a pass of the trimmer.A slim design offers more visibility in front of a mirror and allows you to better monitor where you’re cutting, but a too-slim design can be difficult to grip securely. A slim, robust design: We like trimmers that are slender in shape but also durable enough to last years without breaking if dropped.