I have the bottom of the range Garmin Etrex. The simple yellow one, now replaced by the similar Etrex H. It doesn't have any mapping built-in but simply allows me to follow a pre-planned route.

I bought the GPS unit after doing one 200 km audax (randonneuring event) working from a route sheet. I found having to constantly monitor the sheet and my bike computer to work out which turns to take was stressful, error-prone and completely spoiled my enjoyment of the ride. I like to look at the scenery and relax when I'm out on my bike.

Discovering that even many of my very experienced randonneuring pals still took wrong turns on a regular basis convinced me that GPS was the way to go. I bought a copy of Memory Map with a digital map covering the entire UK at 1:50,000 scale and use that to plot all my routes, but there are lots of websites that allow you do that online. When I'm finished, I upload the route data to my GPS and I'm good to go.

I have navigated well over 10,000 miles of organised rides with the Etrex now and the only times I went off course were when I was busy talking and forgot to look at it.

I know many people who use more advanced GPS models with onboard mapping. They are useful if you like to improvise routes out on the road, or if you find your planned route is blocked for some reason. (I got caught out on a 140 mile ride home from a family visit when Snake Pass was closed for resurfacing. Fortunately, I knew an alternative route to bypass that section!)

I highly recommend navigating by GPS, but I'd always suggest that you carry a paper map too, just in case.