boooooooooIt just looks nice(r?) and feels heavier.
The 800 has a retractable tip, making it more portable. It's often reported that the leads feel loose and break more often, but YMMV-- apparently it's not a problem in all of them, or at least not noticeable to some.
The 600 is cheaper, but does not have the retractable tip.
I have the Uni Kuru Toga 0.5mm and the Rotring 600 0.5mm, and I really like the weight more in the 600 than the Kuru Toga. I can't speak for the 800, but I would assume it is at least as heavy. The UKT has the whole lead-rotation thing, but honestly, I've never noticed it in use.
boooooooooAll metal means that it feels nicer when writing and is heavier. In addition, knurling grip is always better than not. Tip is also longer, which helps out when drawing. Honestly, you can just buy the cheaper Rotring 600 as well, which gives you much of the same (except of the retractable tip).
tr4656If you're clumsy, be careful with the Rotring 600 because a lot of people have broken the tip (after it fell off their desk, etc.) and we don't sell replacement tips.
The 800 has a retractable tip, making it more portable. It's often reported that the leads feel loose and break more often, but YMMV-- apparently it's not a problem in all of them, or at least not noticeable to some.
The 600 is cheaper, but does not have the retractable tip.
I have the Uni Kuru Toga 0.5mm and the Rotring 600 0.5mm, and I really like the weight more in the 600 than the Kuru Toga. I can't speak for the 800, but I would assume it is at least as heavy. The UKT has the whole lead-rotation thing, but honestly, I've never noticed it in use.