Should I buy it?

As an actual owner of a similar thing: no

The problem isn't even how much water comes from there (you can figure it out and not set the water jet to full power), but rather that you are expected to insert this thing back and forth, which, trust me, you won't do since your anus is unprepared, unexpanded and, well, dirty.

So, while interesting on paper, this thing doesn't really work the way it's intended to. There you have it!