I have been using three Glasstran guys on the upper set of 100 feet of Rohn 25.
This is my 160-meter, series-fed tower which is lightly loaded at the top with
small 6 meter, 2 meter and 1.25 meter antennas.
Glasstran is the predecessor of Phillystran. It is fiberglass material covered
with a thin black sheath for UV protection.
Back in January one of the guys failed, somewhere near the middle. It just
pulled apart -- there were no tree limbs or anything nearby to chafe it.
Fortunately I had a calm day and after loosening the other two guys in the set
I replaced the broken one with a new one made of EHS steel with insulators.
Yesterday I found another of the Glasstran guys broken -- this time right at
the bottom end fitting. This and the other remaining Glasstran will be replaced
with steel as soon as weather permits.
I don't know what the expected life span of this material was, but it obviously
has been exceeded! I purchased a 500-ft spool from Phillystran in the mid-1980s
and it was used then for about 6 years, then kept in storage for about 6 years
till reinstalled at this QTH 5 years ago.