Blossom set spray was devised to be used where there are cold springs such as in the PNW where it's often too cold to get good self pollenization. It works by inducing what's called parthenocarpy which means that ovules in the tomato ovary, seeds to be, do not need to be fertilized by pollen.
The downside of that is that fruit development is abnormal and it's possible to get malformed fruits that are sometimes mealy, and it also means that there are very few seeds which is important to those who do save seeds from OP varieties.
If lack of pollenization is due to high temps or otherwise bad weather the Blossom Set spray can't do a thing to help/ The active hormone ingredient is different depening on the specific brand but the most common one is IAA, which is indole acetic acid, a plant hormone.
To answer your question directly, no, I have never used it, and won't be and I also wanted to add that Dr. James Baggett of OSU has bred several parthenocarpic varieties for the PNW and the best known one is Oregon Spring, which I did grow many years ago.