The saddle joint needs caulk or Duct Sealant...Soldering any great length would become onerous and, as discussed above, toxic. I will likely have up to a dozen saddles — and with variable gaps plus the seam length in the conduit (am not using spiral or PVC) soldering would be one a major problem. Caulk/aluminum tape seems efficient and cheap. I can put aluminum tape on 20’ of seam very quickly and be up and running. Caulk is similar, but with a drying time. I dare say that 20’ of soldering would take some time.