I had two in the space of 9 years. A -94 that was running fine with 30,000 miles on the clock and a -99 that was dead with less than 40,000 miles due to waterpump failure and a warped head.
Take a good look a this particular bike. If there is any water in the oil (chocolate brown) the water pump seal is about to fail. This is a half hour £50 job, unless the owner hasn't fixed it and has wrecked the engine. Take a multimeter and check the voltage to the battery with the engine running. Any odd numbers and the VR is on it's way out. Take a really good look at the condition.
The chaingang website is the place to look, but without upsetting anyone does suffer from the usual single marque club, rose tinted glasses. These bikes are Aprillia designed '90's bikes, not classic BMW's. BMW learned everything they know about cheap metal and thin paint by building these bikes. The carbed F650 is a modern BMW, not a last a lifetime/never stop R80 or R100.
If this bike is fine and you are happy with the idea of carrying and using a waterpump kit as required, dealing with two carbs and four valves, needing the electrics to work etc, then go for it. If you are not or the bike isn't good, hold on to your cash until something Japanese and/or aircooled comes along.