If you’re just after a basic easy to use computer to measure time, distance, and speed, then the wireless Bontrager Trip 100 does the job perfectly, or the Trip 200 to add temperature and a backlight. Both include all the sensors and batteries and are ready to go.
To start getting more technical and measure heart rate and cadence, go for the Bontrager Node 1.1, or the Node 2.1 to add temperature, altitude, and gradient. The speed and cadence sensor is not included for either of these models, so add those if you need them. The 1.1 doesn’t come with a heart rate monitor strap, but the 2.1 does.
The Lezyne Mini GPS, as the name suggests, include a GPS unit, to allow you to track where you’ve ridden and upload to your computer after the ride - no sensors needed, it all runs off the GPS, just attach to your handlebars and ride.
Unconditional Bontrager Guarantee - all Bontrager computers come with a 30-day trial period, if you don’t like it, return it for a no-quibble refund.