The Parker gel pen writes very smooth and bold, with a rollerball feel. My gel pens have the titanium gold finish that will not wear off. Most handmade wood pens have a gold plate that will wear off in a short time.  The titanium finish is created when two lasers are pointed at two disks, one titanium and one gold, and the resulting vapor is deposited on the pen, resulting in an extremely hard finish that will not buff off, even after a minute of buffing with rough compounds.  It just gets shinier, while a gold plated finish will disappear within a second.

Parker gel refills are available in Black (30525) at Office Depot, both Black and Blue at Staples,  and in 4 other colors at pencity.com, including turquoise, green, red, and purple. The refills usually cost $5.00 for two.

I use only genuine Parker Gel cartridges.  The buyer can look at the cartridge to see which one to buy to replace it with.  As far as I know, I am the only pen maker who uses genuine Brand-name cartridges in my Space pens and Gel pens.  Most pen makers use the generic refills supplied with the parts they buy.  Those refills write well enough at the beginning, but seem to stop writing after a month or so, even though still full of ink. My genuine refills cost a little more, but in the case of the genuine Parker Gel, the genuine refill ink will not smear (helpful for lefties), while the generic refills will smear.