Many manufacturers have less than tight upper/lower fitment. Size an accu wedge for the receiver shelf height you have and it will reduce if not stop all receiver wobble. That is if it really bothers you.Im not going to comment on the above for fear of an infraction.
But, I helped a friend put a pistol together using the spikes upper and lower. They fit together like ****. Rattled horrendously. He ended up buying shims and put them on the pivot pin to tighten it up. Looks cool, but not sure if its worth the $450 for just the lower.