actually using caliper cover has its use to prevent brake dust accumulate on ur bling2 rims.
if ur car like mine, 2 front disc and rear is drum brake, then without the caliper cover, the front rim will be dirty with brake dust and rim looks dirtier than the rear ones... if all dirty, then dirty together with same tone.. after use the cover, the front rims stays clean and same tone with the rear rims. the caliper seems to divert the brake dust to other side of rim...