Used them many years ago when I had only a few plants and agree with what Matilda posted. Mine began to grow algae in the tubes and were hard to clean. Then they began to leak and I had to buy replacement tubes. Got tired of the hassle because they didn't really gain me that much in terms of early harvest. The plants didn't freeze but also didn't grow much when the ground and air was still so cold.
Have to add that some people really seem to be happy with how they work, though. YMMV.
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