Haven't used them but I've seen them - If you want it to look flawless to the most critical eye, go new. If you don't mind that someone really picking might notice up near the windshield frame or on a side (really, really picking) that it's a cover, go with the cover. Went through this with a '69 mach 1 bought the cover, learned my lesson, then bought the pad.
--OR--
look at it with the pad off for a while and see what you think. My pad was cracked and I never put it back after paint. After seeing it without the pad for a while i really like it better and have no intention of ever buying a pad.