I have put 5K on the set I installed on my toyhauler. I can tell you that it does ride smoother now. How much smoother is hard to quantify. Maybe 20-30%? But I can tell you that Iam sure there is less rattling going on inside the trailer when Iam moving.
Liked it so much I just installed another set on my fiver. About to make a cross country run with it of 6K+ and I have little worry about my suspension system now. Strangely enough, even though I replaced the original wet bolts with the whole new EZ Flex system, I found that my old brass bushings were wearing thin after 30K on the road. So my upgrade was timely and not all that expensive by comparison. However, I did do all the labor myself.
Looking forward to towing with my new EZ Flex system on the fiver.
I looked at some of the more exotic new suspension systems, but was put off by the reviewers too often talking about they couldn't do this or that to their new system when they needed adjusting or repair. To me simpler is always better.
Good Luck which ever way you go.