I own this:
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I have pitched it with my tarp a few times...as a trial to see how it would work and how i would go about using it. Interestingly enough I never used it on a trip. I have too much other gear that made this item obsolete (so far)
I also own the HMG Mid Half Insert that I have actually used many times on trips ranging from hiking, to backcountry ski touring to bicycle touring. It works reasonably well...there is one other thing about single wall tarps/tents ... you get misting on the inside when it is raining or wet...you are in your sleeping bag and receive either droplet drips on your face or feeling of wet mist.
It is somewhat moot point if You spend several days in a rainy environment...pretty much every shelter and every item in your possession will be wet.