Installing the insulators is a cost (probably not a risk...).
The big disadvantage of cutting up the backstay to install 2 isolators (a single
stay or a split one like in your case) is - as stated above - that you have no possibility left to change the length if the auto tuner encounters tuning problems on some frequencies. OK you might lengthen or shorten the GTO-15 or similar wire that runs from the lower insulator untill the antenna tuner but that will have its limits.
I am also using a permanently installed "alternate backstay antenna" - the Bill B.Trayfors design. Total length (sloping wire + the wire connecting it to the antenna tuner) is 9.2metres. This favours frequencies from 7 Mhz untill 21 mhz but my SGC-230 atu tunes every frequency between 2.2 Mhz and 30 mhz.
One might argument that in your case the lower part of this alternate backstay wire would run close to SB or port lower part of your split backstay hence coupling into it, distorting the radiation pattern etc. This even goes for the alternate stay versus a single wire central backstay. Bear in mind that on HF frequencies every sloping wire antenna or even SSB
whip (backstay or other) is close to the rest of the rigging
, coupling into it, distorting the radiation pattern.
Summing up, I can advise you the alternate backstay antenna:
insulators, ss wire or HD insulated copper litze, one isolated through-hull connector)
- can be built for sturdy permanent installation
- length can be trimmed easily before deciding on definitive length
- needs no or few standoffs to lead the GTO-15 (or alike) wire to the antenna tuner