A black cloth is definitely the best option if/where it is practical; it provides a nearly complete black out.
Our shade shade can't provide anywhere close to the black-out power of putting black cloth over both you and the subject, but still modestly improves the viewing experience and is convenient for situations where a black cloth would be cumbersome or otherwise impractical, and it was designed to take up zero additional room in your pack (by being reversible) and almost no weight (it's carbon-fiber composite material and quite thin).
TLDR:
Black cloth: maximally effective, moderately practical
DT LCD Shade: moderately effective, maximally practical