I'll be watching this thread also. I still am not sure about the differences between gel and regular ink... or between ball and rollerpoint, for that matter.
If anyone can shed some light here I'll be more than grateful.
TIA
The real differences are in the ink.
A gel uses a polymer type of carrier and uses opaque pigments for the color.
A ball point uses an alcohol carried dye and a roller ball uses water based fountain pen inks.
They all have a different feel when writing and a gel is (I think) better for slick and less absorbent surfaces than a RB or BP.
Gel and RB run out of ink faster since they lay more down.
RB and Ballpoint inks are usually relatively easy to wash out of checks or legal documents and less secure than the pigment based gel inks which cannot be washed out by any normal means (if any) from most paper.
I think most people select from the three by the way it feels and the color rather than security reasons, but if you are pushing a gel it is a good sales pitch about it. Same for archival quality ink in a dropper fill or cartridge conversion RB system.
This is, of course, from my limited understanding and stands to be corrected by anyone with greater knowledge.
