If you look at this post and my previous post, you will see the strong correlation in between these two cryptocurrencies. I know that the hole market haves a correlation, even though that correlation did decrease, XLM and XRP seem to always move in the same direction. Knowing XLM is 1/3 the price of a XRP could be a smart investment. Now this is obvioulsy not a good enough reason to invest, but if you like the XLM crypto for what it is too, then it could be a wise move.
I say this, however I have not invested in it myself. It is just something to think about.