This may be another YMMV situation. I use a mylar blanket slung under my hammock. Yes, it is noisy, but one can last me all season and beyond. Also, I just returned from a trip to FL. On my bucket list was camping at a waterfront site in Fort DeSoto (County) Park. I used a space blanket under my <$20 (well-known bidding site) tent. The base was mostly sand with some small shells. Even with moving the tent, between sites, the space blanket looked pristine when I put it away. No, it did not fold as small, but it at least was the same weight.

That said, if you have the opportunity to use Polycro, my opinion is "Go for it," unless you are in a sun-baked situation. I also used a one of these blanket under my tent in the Grand Canyon some years ago. With afternoon temps reaching 120 F, the ground didn't cool much before about 1 AM. The first night, the heat was somewhat reflected away from me, the second night (not moving the tent) the ground hadn't heated under the tent.

In windy conditions, you may find it easier to spread the lightweight blanket after erecting the tent, then working the blanket under it.