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Depends if it meets your needs, the etrex 20 is more cost effective if you do not need such things as barometric altimeter, 3 axis compass and wireless sharing.
The 20 and 30 are identical in all other respects. I have an etrex 30 but only by default as i managed to pick one up very cheaply second hand . For my usage, mountain biking and hiking the etrex 20 would have been perfectly satisfacory.Depending on your needs and proposed usage do not rule out one of the older etrex units such as the vista or legend HCX. You may be able to pick one up fairly cheaply.
Disposable battery powered garmins;
Is the Etrex 30x the best shout?