I use an Edge 200 and a Sony Xperia Active for navigation...
In favour of both:
- they are both a nice compact size
- they are both waterproof
- they both have solid handlebar mounts
- both can be charged from either a USB battery or a dyno USB charger whilst riding
In favour of the Xperia:
- you can be logging direct to the web as you go, and/or as soon as you finish
- being Android, you can customise the nuts off of it, so:
- you can make the maps highly visible in any light (I have a map style which is far clearer than any other I've used)
- you can get applications which adjust the GPS polling to conserve battery life, to the point where it will go as long as an Edge provided you have the screen off most of the time
- you can get the screen to display the info you want
- it is futureproof, you can adopt any new logging/mapping/navigation app that comes along
- uploading/downloading maps/routes/etc can be done wirelessly, instantly, and (almost) anywhere
In favour of the Edge:
- for most people, it will cover any ride on a single charge at full logging detail
- it has buttons instead of a capacitive touchscreen, making it easier to use with gloves and when covered with water (that said, I can set the Xperia up so that a single press on the lock button goes into the map view)
- it's cheaper (though of course this isn't true of the 800)
- the 200 has no navigational alerting at all, you just follow a wiggly line
In reality I think 90% of the time, the Edge for following a planned route plus a smartphone for maps when you need them is the easiest way. I've navigated a 360-mile route on unfamiliar roads with the Xperia and it did admirably well, but for more local rides it's probably overkill. That said, the fact that an Edge makes you dependent on a PC makes it feel like last century's technology IMO.
The smartphone can be a good solution if you get the right one (eg, only the Xperia has a bar mount I'd consider using) *and* you're prepared to faff with setting it up and finding apps that work for you. If you're less obsessive about setting stuff up and prefer to just go with what Garmin think is best then the 800 will suit. If you'd prefer not to pay for the 800 then the 200 plus a cheap Android phone would give you pretty much the best of both worlds, provided you're happy with not necessarily having maps always visible on the bars (that's the big ask, and that's where the 800 comes in).