When I got the 2006 Subaru outback there was no shelf depth or room to suction mount my old faithful 4" NUVI within the instrument cluster; I used to mount it to the left of the speedometer over the tachometer gauge in the 1998 Legacy. I got used to the convenience of glancing quickly through the steeringwheel at Map view when on city/town streets for the surrounding view - very useful in twisty loopy suburbs. It never failed to get me accurately to any location I would input all over Canada and the USA and you can toggle between fastest, scenic or shortest routing (which tends to take you down winding gravel backroads around here rather than the main hiway - :-()
I don't like mounting a GPS to the dashboard top or window in plain view of interested parties...and prefer to keep my eyes on the road ahead other than glancing at the speedometer. I also appreciate things neat and tidy without cables snaking everywhere for that built-in look.
Most newer vehicles now have a Navigation Screen option and therefore a space is provided in dashboards in a central location between the airvent outlets. My Outback did not come with Navigation so the 'hole' in the dashboard is a 6" deep cubbyhole with a flip-up lid.
Just for kicks 12 months ago while making other 'improvements & upgrades' to the interior I decided to audition the latest GPS's and liked the larger 5" widescreen models 'cause these old eyes ain't getting any sharper. Our local Staples allowed me to take 5" Magellen, Tom-Tom and Nuvis out for a test drive and test fit. No contest - The Garmin NUVI has more information, a less cluttered desktop and the form factor is superior in that it is a plain .5" thin flat rectangular box that slips easily into a pocket like an iPod. The Magellen and Tom-Tom have curves and case protrusions that make then lumpy and larger.
In happy co-incidence the NUVI slips perfectly into the dashboard cubby with a 'c-hair' to spare in width...meaning I can keep it hidden and stored behind the flipdoor between uses along with car ownership/Insurance etc. The competing GPS's were too wide.
For use I put a strip of industrial velcro on the top edge and a corresponding strip on the lid lip. The lid springs are strong enough to hang the Nuvi from without drooping.
I installed the power supply hidden inside the console housing - adding a remote switch - and ran the cord up behind the dashboard and into the cubby from the back, for hidden and quick connection and charging. This also means when I stop briefly at a store, gas station or wherever, I can hide the entire thing inside the cubby away from prying eyes without shutting it off.
Because Staples, Best Buy and FutureShop only stocked the Silver version I went to Tiger Direct and got a refurbished Piano Black Model 1490T for $130 CDN.
It does have Bluetooth capability which is utterly useless to me but the bonus is it came with the Traffic Antenna power cord free (an optional accessory from Garmin) and it really works to alert you to traffic tie-ups, accidents, construction detours, Photo Cameras etc. Very useful on my last trip across upstate New York as was the Speed monitor that tells and alerts you what the posted speed is as you pass through the zones on those two-lane back roads through villages. Last thing anyone needs in a Turbo is unwanted speeding tickets.

With this facility I can punch the Cruise Control and drive unconcerned.
I have found that when I go 'off-route' the Garmin very quickly re-maps itself and accepts my notion of ignoring its suggestions.
Not one to take orders from some snippy woman I downloaded a sexy Australian man to tell me where to go.
Although this model does not come with lifetime updates it does have one free one and I love the NUVI look and feel so much I will not hesitate to pay Garmin $50 whenever they suggest it as when I drive across the USA and Canada on long trips in the next 10 years I know new suburbs and streets are being built constantly.
The thin Garmin NUVI is also an excellent pocketable handheld for wandering around city streets on foot in Pedestrian Mode.
Recent 'laws' require GPS's by default to disable certain touchscreen functions when in motion but the Garmin has a toggle that defeats this annoyance and keeps it set that way when the unit is turned off and on again.
So I say, go to a shop that will allow you to take one out for a test drive, evaluate it's features, form factor and user friendliness, then go online looking for mail order bargains and make an informed purchase of the model you want.
Dave
