This is something you need to decide for yourself. Some people like fenders and others hate them so asking this type of question you will get all kinds of opinions which are only based on personal preferences. For me personally I've been riding with full fenders for almost 20 years and they are one of the most practical accessories I've ever put on my bikes. Fenders won't keep your bike perfectly clean but they will keep you and your clothes clean. if your goal is to keep yourself clean then get fenders. First thing you need to check is how much clearance there is between your 40mm tires and the frame / fork. Do you even have enough room for fenders without your tires rubbing ?