I've had a 2002 model from new, that was when the main mods were done on the carb 650 (engine internals, headlight, panniers, linked brakes etc). The 700 injected version came in at 2006.
The early panniers were pretty small, the later 650 ones were only a bit better. You can get big lids for them (if you can find them now!). Weather protection is pretty good with the high screen, hand wind deflectors etc. Most people find the standard low screen is awful, directs wind straight at your chest. Early headlight pretty awful.
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They do exactly what they look like, a bit heavy, not exciting, handle fine for what they are, brakes are decent if working properly, only a few weaknesses/faults mostly easily fixed (fuel pump points on 650, head bearings if not greased and adjusted properly etc). If serviced & looked after they'll go on for ever, couriers do typically 150k miles plus before they get too tatty. Getting the rear wheel out of the 650 is easy peasy, the rear part of the mudguard comes out with a few screws and the wheel rolls out the back. The 700 isn't as easy.
They get run-in at around 20k miles. I've just done a trip to sunny Scotland on mine, 360mls in one go is no issue at all. Black forest trip in late May, no problem. Never had to lube or adjust the chain once
Fuel cons at legal limit cruising is just about 60mpg, most people get 55-60mpg. Tank range 180-200 before reserve with another 20 or so reliably.
Condition is everything. Personally I wouldn't go for the early one, but some people prefer them.