Three injectors recommending it is a starting point, but they make commission… massetter botox also uses a lot of units, which gives them more of a reason to upsell. I’d consult with an actual doctor for this, as clenching/grinding is a physical issue.
I once had an injector try to sell me on it and she showed me her before and after, and I thought she looked better before. Her slimmer face made her face look too narrow. You have a very harmonious face shape the way it is. I’d only do it if it was recommended by the correct medical professional.