GPS tracker for hiking

Hopefully I have put this in the right section. Has anyone had any experience with these please? We are siting our van on the edge of Dartmoor and are planning several walks on the moor. As you know, the weather can turn very quickly and I would feel a lot happier if I had a device to guide me in the right direction. I have purchsed a book of 20 suggested walks which give coordinates for every way point so we should not get lost! Suggestions of a suitable model would be welcome. Thanks.