It doesn’t seem to be popular on SDN but I found it very helpful in my Step 1 prep. Like you, I started it after I finished uworld. It’s not a qbank that will teach you how to think (that’s what uworld is for) but it’s good for drilling in high yield concepts. Everyone learns differently, but for me it was useful to see the same concepts presented in a different way, it definitely made me test whether I truly understand them.
As to whether it’s representative of Step 1, I don’t fully remember (repressed that day from my memory), but I think Rx has a higher number of straightforward questions. To me real Step felt like a mix of Uworld and NBMEs. However, concepts tested were all the same across the different resources.