Both the units are similar in many respects. Both these units are rugged and waterproof and come with preloaded maps. It also has the ability to add additional maps and points of interests. Both these units come with an internal antenna that is integrated with a highly sensitive receiver. Both allow you to add waypoints or favourites; while the Zumo 550 permits you to add just 500, the 600 provides you with double the limit. Both these units provides you with timely and regular voice directions along with apt visual instructions. The Zumo 660 however has a wider 4.3-inch screen as compared to the 500′s 3.5-inch one.

As far as entertainment goes, both of these devices come with an internal MP3 player, an audio book player and a picture viewer. Also they are compatible with Bluetooth technology for hands free calling. You can plug your headphones to the jack provided to listen to the route instructions as well as your favourite music tracks. Also they come with Garmin Lock feature that is an anti-theft feature, which is used to safeguard the information from unwanted users.

Though there are so many units, the Zumo 660 is equipped with a few additional features that gives it a upper hand. It has a lane assist functionality that is absent in the Zumo550. Also the 660 can display the major building and landmarks in 3D formats providing you with a better orientation and view of the place. While the Zumo 550 does not have a speed limit indicator, the 660 has this function. This prevents you from being pulled over for speed related issues. Also the Zumo 660 is slimmer and lighter as compared to its predecessor.

Priced below £529, the Zumo 550 is definitely a value for money product if you are not after the advanced functionalities. But if you want the high-end features, then the Zumo 660 is worth the £549.99 price tag.

There are dual sat navs that serve both these purposes. The Garmin Nuvi 550 and Road Angel Adventurer 7000 are two such adventurous GPS systems that can be used as automotive sat navs as well. Both of them come with a 3.5-inch display screen and a waterproof and rugged body. Also both are similar when it comes to the battery life, they both run on rechargeable battery that lasts for 8 hours. Both these units provide you with spoken directions along with visual route information.

While the Garmin Nuvi 550 comes with an internal solid state memory, the Road Angel 7000 has 1GB of total memory capacity for storing maps and other data. Both these units provide information speed limits but the Road Angel is capable of identifying most of the safety cameras. While the Garmin device can be used for marine navigation, the Road Angel is incapable of providing this kind of information.

Furthermore, the Garmin unit comes with Garmin’s patented features that include a “Where Am I?” option, which provides you with the latitude and longitude information of your position along with the nearby hospitals or police stations. Other add-ons include an anti-theft functionality and the World Travel clock, currency and unit converter and a picture viewer.

Whilst Garmin is scoring on these points, the Road Angel is not to be left behind. It has managed to incorporate an MP3 player and Bluetooth technology in its unit. Thus is is a favourite amongst all those who have an affinity for music. Like its Garmin competitor, it includes a picture viewer for viewing photos or friends and relatives.

Both these units have their own plus and minus points. Basically, both these units are able to perform the dual function of being an in-car satellite navigator as well as a hiking GPS guide. It is advisable to have an idea of your personal requirements in a GPS unit and then weigh the pros and cons before zeroing on any one unit.