It’s interesting that they still produce, as hybrids are supposed to be sterile.
Nah, most hybrids will sprout just fine. They won’t, however, generally come true. Ie, those ‘better boy’ tomato seeds will probably produce whatever parents or grandparents the better boy had. They’ll also be a mixed bag of disease resistance, timing to production and size. With a small possibility they crossed with the ‘big rainbow’ you had planted right next to them. Course, if you chose the hybrid for disease resistance it won’t do for you to plant seeds that might not be and waste your time/space on plants that just die at a whiff of Fusarium.
Some hybrids will come true at the same rate of OP though. ‘Santa’ grape tomatoes are an example. Since they don’t sell the seed for those anymore (I haven’t found it lately), most people just buy ‘Sweet Santa’ or something similarly named (it has several names depending on the grower) in the grocery store and save those seeds. Santa will come true 99/100 of the time.
Very few hybrids are sterile, they’re just a gamble. There’s no way to predict which of the parent genes it will inherit.