I'd suggest the Zarc Industries Vexor Micro-Spin in mark III or mark IV. It's very powerful & in use with a few large LE agencies. Check your local-state laws. You may not be able to own/buy it in some locations.
Sabre's new Green style is hot too. It's a Wasabi type formula in a hot format. I own the Sabre Red Crossfire Mk III now.
Cold Steel's Inferno line is hot & is available to most citizens.
A brand/style with a UV dye(for subject identification) is good.
Many working cops corrections & security guards avoid the foam styles.
Subjects can flick or fling the goo back at you or rub it into you in a confrontation.
Zarc's new R&Ded micro-spin format has merit.
Gel or sticky types aren't bad for indoors(parking units, garages, malls, medical centers).
Have them take a formal class or skill training too. It will build their confidence & if they deploy the OC in a real incident, the training is documented by respected instructor. And yes, OC spray hurts!
www.coldsteelaz.com www.qmuniforms.com www.galls.com www.policehq.com www.uscav.com www.natchezss.com