I got my TWSBI Mini on Monday.
It's my second fountain pen, the first being the Lamy Safari, and first expensive (for me) pen purchase.
It's a gorgeous pen and it writes perfectly smooth. It was shipped extremely fast (2 days after I ordered it)
Whether this pen fails/cracks or not within the next 4 months will determine whether or not I buy the 580 when it comes out.
The TWSBI mini was also my first nicer pen. it writes beautifully and is still one of my smoothest EF nibs.