Note that this does precisely what it says - expands to 4ft x 4ft - and nothing else. I misread the description and assumed that it would expand to any square size up to 4ft x 4ft. I was wrong.
Because of the way that it’s built, it expands to 4x4. Using it at any smaller size is not safe because it will tend to slip to 4x4.
Not a complaint, but a caution to anyone (else!) that read the description the way they wanted to rather than exactly what is written. 
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thanks for this comment - i needed to know this before purchase!