IIRC the vortilons developed on the HS 125-800 (some of the first to be used?) were relatively small (also see Gulfstream a/c). The objective was to replace wing fences used on previous models, which minimised span-wise flow and tip stall, and predominantly maintained aileron effectiveness. The -800 used a larger wing than with previous 125s and the ailerons have ‘super-critical’ sections. The standard wing fence ‘fix’ on the -800 required more vortex generators just in front of the aileron hinge line; the combination added drag.
The vortilon solution had less drag than the wing fence and required fewer vortex generators. Furthermore (as above) there were advantages at low speed (lower stall speed?), and possibly with high speed cruise performance.
There was only one set per wing, whereas other aircraft have several.
Photos: Raytheon Hawker 800XP Aircraft Pictures | !!!!!!!!!!!!!!