Throwing all proper methods of experimentation aside, I'm going to offer up my review of two products that I began using simultaneously, so take my experience for what it's worth.
I've been meaning to buy/try a pair of Nike Frees for a long time (years). But they're kind of pricey for me to just try, so it was an item that stayed on my to-do list pretty much long term. As I've been obsessed with attempting to clear the list for the last month or so (since I have nothing else to do) I finally bought a pair. A few years ago I could easily go to the Nike web page and even design my own colors and everything. The last few months however I had a hard time even finding a pair. I'm not sure if they are discontinuing them, re-designing them, or what. If they are being changed/eliminated, I certainly didn't want to pay much money for a pair, so I search Ebay and bought a "minimally used" pair for $20 (including shipping). The web site cautions about being sure to increase a person's use of them over a period of time to "acclimate" to the reduced support the shoe offers, but I've never been a fan of that, so I jumped right in. Wearing them around (like I am today at work) all I notice is that they remind me of the $5 Target slip-on shoes I lived in for many years as a teenager. Very comfortable. I did a 10 mile run in them last weekend and I notice I run with a much lighter step. When I ran 10 miles the next day in regular shoes I felt more "clumpy". I haven't been extra sore or had new muscle soreness. I did notice on Monday morning getting out of bed my feet bottoms were a little sore for a few minutes until they "stretched" out, but that happens occasionally regardless. I also had a little knee pain on Monday during the day, but again, I leave for Wyoming tomorrow and before any race or big trip I ALWAYS have weird phantom pain that is nothing really; probably just me being extra in-tune with my body as I prepare for an event.
My treadmill is great thus far. Just wish I had more time to use it this week. It's a MUCH better treadmill than my old one is all ways, so I don't foresee it causing me trouble.