Do the various single-lap roof slate systems, that use non-slate materials beneath roofing slates to achieve a water-tight roof, provide a similar benefit to SlateSpacer™?

No — apples and oranges. SlateSpacer™ increases roof and slate life — single-lap slate systems reduce weight. A roof is only as long-lived as its shortest-lived element. SlateSpacer™ is made of stainless steel, which matches slate life. The water-shedding components of single-lap slate systems are made of fabric, plastic, or galvanized steel, which do not last as long as high-grade slate and cannot extend roof life (but they are well-suited to the aim of weight reduction). Another distinction between the systems is that SlateSpacer™ is designed to minimize capillary action around the part itself. The elements of single-lap systems are not: like slates, they provide a lengthy capillary path. Because of how the elements are situated, capillary action can extend nearly the full length of the slate. (It should be understood that while single-lap systems do not minimize capillary ascent, the overlaps used by the better systems do prevent water from entering the building they cover, just ...  more