This is my best fountain pen. It looks like a Lego pen, but who am I to complain? It's got the best inkflow for a $20 pen, even with a fine nib. It's very sturdy. It leaks a little bit sometimes into the cap, but this may be a common thing for fountain pens.
My only complaint is that I'd prefer it to be smaller. This is a beast of a pen.
It includes the adapter to fill up from an ink bottle. I'm not sure if this is a standard feature for all fountain pens, so I thought I'll mention this.
The only slight shortcoming of Core is that the nib is very rigid. I really love flexible nibs but Core's huge nib feels like it's carved out of a diamond.