Internal heat reflective blinds

Has anyone installed the internal roller blinds that reflect uv and heat. Don't know what they are called but come in several colours and plain (the ones I have seen anyway). The claim is that 75% heat is kept out and you cant seen in unless light is on. I can't find any information that says whether they are worth getting or not. Have heavy drapes, pelmets and outside shade all which has proven highly effective in the heat. But would prefer to keep the drapes open in summer when home so am...

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