This is a super piece of kit for measuring your bike speed, distance covered, average speed etc and it is reliable. The hardest task is setting it up initially and calculating the wheel coefficient (ie diameter of wheel x pi) which is worth noting down because inputted data is lost when the battery is changed. After setting it a few times, it becomes second nature and takes only a minute for subsequent setting-up and then you're away. It's fun to use and, for the less fit such as myself, it's good to see my distance increasing daily while also being encouraged to go a little further on each trip.
I've used mine in a light shower but I'm doubtful whether the handlebar unit would withstand a thorough British winter drenching. I get around this by removing it from the handlebars and popping it into my pocket where it still receives a signal from the transmitter unit on the fork.
I note some reviewers didn't get a reading from their unit - nor did I initially but this was my own fault. I'd incorrectly fitted it with the spoke magnet pointing away from the receiver unit on the fork! Once I realised I turned it around and it worked perfectly and has done ever since.
A good buy.