I carefully tested two identical hoses, and they both failed miserably.  In the range of 15-20 PSI the flow rate is absurdly low, and parts of the hose that are in the sun warm up enough that the hose softens, expands, and lets lots of water out at that place.  At higher pressure (40 PSI) more water comes out of the soft spot(s) and most of the rest of the hose still barely lets any water out.