I was thinking of getting a 10 box of these 10oz bars . They are a bit higher priced than other 10oz bars .Was wondering if they would still be a ok investment or would they be more inclined to tarnish because of thier coin like finish ?.Any advice would be greatly appreciated.https://brisbanebullion.com.au/10x-10-oz-queensland-mint-silver-minted-bar-slab