I love mine, for the price, it is outstanding. I would never have expected it to perform so well. Smooth on most kinds of paper, huge reserve of ink, never leaks (ok it did once but that was so my fault).
Just got my first 580 two days ago but have not written with it. i also got the new Eco T and have been writing with that. So far love it and it’s a great pen! Demonstrators are great. Especially affordable ones.
Have two Ecos'--use 'em every day in many environments that are less than ideal, and for the most part, they haven't let me down (of course you have to be careful of dramatic changes in altitude--that can be ugly), otherwise I like them as much or more than any other steel nibbed, plunger-filler on the market for well underv$100--and there are damn few!
The ink compacity for twsbi is amazing across the board. The ecos are my favorite, and great for starting out in the fountain pen collection.
I own a twsbi vac 700, not the vac700R. The pen holds a lot of ink, but it has burping issues when the pen is less than half full. I've tried it with many many different ink varieties, (and those of you that haven't tried Sailor's Kiwa Guro, you're really missing out) and found that it burps (drops a blob of ink when you least expect it). The upside is, it is much easier to clean.