I like the look of the Silver Helix wheels, but I also like exposed lug nuts. It's putting me in a quandary between the Helix and the standard Silver wheels. I like the pattern and rim on the Helix better, but I like the exposed lug nuts of the Silver wheels better. What does it look like behind that cover of the Helix? Would it look bad to leave it exposed without installing the cover? Is the cover plastic?