Is FaceTite superior to multiple rounds of Trusculpt for double chin?

anything internal will be better than anything external like trusculpt.  facetite + liposuction will also give you contouring and shaping (see link) but this need sto be done by an expert as I have fixed a lot of scarring and burns when this is not done properly.
With significant neck sagging you would need a neck/face lift with muscle tightening (platysmaplasty). at the same time lasers (fraxel,  co2 or erbium( or microneedling RF (fractora, intensif) can be . performed to improve the crepe skin or wrinkles.  You need a formal consultation, as the neck can be treated with a combination approach:
1. micro needling and lasers for texture
2. botox, disport or xeomin to help platysmal bands
3. intensif or fractora RF microneedling for crepe skin and lifting
4. fillers like belotero, restylane silk, juvederm volbella to improve lines and folds
5. neck/face lifting if sagging is prominent or early starting +/- platysmaplasty (muscle tightening)
6. J plasma/Renuvion, thermiRF, inmode facetite for internal tightening
7. ultherapy and thermage for external tightening
8. regular Venus legacy, exilis ultra, or inmode forma treatments with facials to maintain tightness
9. PDO novathreads or silhouette instalift cone threads for lifting and long-term collagen production
see an expert for a full evaluation and treatment plan based on your individual situation and goals.
Best, Dr. Emer.

If a double chin is due to excess fat, I would say that liposuction is the best treatment for that issue.  If there is excess skin causing a problem, then FaceTite could help to tighten this to some extent, although surgery can usually produce more dramatic improvement.