convenience; user-friendliness
Refers to the quality of being convenient or easy to use, often in the context of services, systems, or products.
The convenience of this app is very high.
We need to improve the user-friendliness of public transportation.
利便性 is a formal word for overall convenience (e.g. of a location or service), while 使い勝手 zeroes in on the hands-on ease of using an object.
Compound of 利便 (convenience) + 性 (nature, quality). The exact historical derivation is uncertain, but the word follows a common pattern for forming abstract nouns.