Hi, no experience with the VDO Dayton systems (too expensive for me), but I did drive around with a PDA and TomTom Navigator 2 (in my case a Dell Axim X5, with cradles and gps receiver supplied by TomTom).
I have to say: very nice tradeoff between installation troubles, screen size and functionality. You get a color screen with a very reasonable size for a price that lies way below that of a B&W system with just an arrow on a tiny screen. Easy to handle, upgradeable
The PDA can be removed (and, of course, be used for many other useful purposes), leaving it up to you to fit the cradle and cables in a nice way. Cabling is just two wires, one of which is better fitted to a power source behind the radio (the cig lighter in between the seats leaves the cord dangling across the gear knob). The gps receiver went slap bang on my dash, but I could see ways to hide the cords a bit more...
I've also read about people mounting the gps receiver underneath the flat surface of the centre console. So inside the console, rigged in between the heater exhausts and the top of the encasing. So that would be out of view too, with good reception.
Well, for me, this was just a trial before I transferred the lot to my mother (who wanted it in the first place). That's another advantage of this system: a simple install can also be taken to another car without a problem. If you get a gps receiver that installs onto/into the PDA (so called compact flash GPS receiver), you could even walk around with your nav system!
I _love_ the wide screen tft-s that slide out of the central console, but at that price, I doubt the value.
Just my 2 cents...
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Edo
(2003 Silver 1.4 Tdi Exclusive(SE), black interior, sport seats, heated mirrors, JVC KD-SH909RB cd-receiver, Infinity Kappa 63.1 + Vifa on-dash tweeters, 12" Subwoofer on 300w Amp)