Hi Fizban,
Just be aware that the first few years had several inbuilt problems that will cost extra to put right. These include a very grabby clutch, a suspect starter motor and variably-poor fuelling. My 2013 821 had all these, but it was and is a fascinating bike to ride with amazing poke in all gears: far more than you'd expect. I run mine on touring mode and the low-speed manners are exemplary, but crack it a little more and you get a kick in the backside, regardless of the gear you are in.
Someone else here may advise you on the years to go for. I think 2016 on, but I may be wrong. All I'm saying is beware of the cheapest bike you see, even if it looks tidy!
Nick, in Norfolk