Well, if it's just for looks, I wouldn't go to the bother of breaking into my fluid lines and then having to do the bleeding etc.
There's also the matter of how well it would sit where the original one is.
Note the advert also says there is a brand name, presumably on the top, which they have photoshopped out. It may be something you'd prefer not to have, e.g a Chinese character. It may be possible to spray black over it.
I can't see the benefit, since I use farkles to make the bike more useful, not fancy looking.
But don't let me spoil your fun. If you're willing to take the pain for the gain, be sure to post pix of the result.