The cross sectional area of 1/4in, 8mm and 1/2in shafts are 31.7mm2, 50.3mm2 126.6mm2 respectively which might explain why panel raiser bits are invariably on 1/2in shanks
Trend do two in their craftpro range one vertical one horizontal. BUT they give quite a narrow raised profile probably OK for kitchen doors and small cabs but not right for a room door.