they remove different things. A skimmer removes dissolved organics before they break down. Read the articles on what skimmers do.
How big is your tank? It's debatable in a nano tank since water changes should be sufficient at nutrient control. There are many large tanks that do just fine without a skimmer and some tanks are so good are removing nutrients they put their skimmers on on off cycles.
They are advisable especially for new folks as new tanks lack sufficient nutrient uptake.
In any case, know what levels of NO3 and PO4 you want to target and match any equipment to meeting those targets.