This article provides a good summary of Blood Flow Restriction Training and important elements of BFR Cuffs. Some key takeaways are:
"A wide cuff is preferred in the correct application of BFR."
"The cuff needs to be tightened to a specific pressure that occludes venous flow while still allowing arterial flow whilst exercises are being performed."
"Simple pieces of equipment such as surgical tubing or elastic straps have been used in gym settings to achieve this result. These are not advisable as you are unable to monitor the amount of blood flow occlusion. A thin diameter may also cause too much local pressure and result in tissue damage."