Gregory Haloscar piloted many different lancer mechs in his career.
During his time with Hysphalin Industries, he bounced from assignment to assignment. Each time, he arrived at different locations and piloted whatever lancer mech the site had in stock at the moment.
Since Hysphalin Industries was mainly in the business of selling large-scale industrial production equipment, it did not really care about sticking to a single brand or mech designer. Every security department of every local branch of the company maintained a different mech roster.
Furthermore, Gregory also polished his skills in simulation training. Though some people treated it was a game, professionals like him piloted virtual mechs as if they were truly real. They fought as if they could only afford a single death in order to make the practice sessions as accurate as possible.