That said, I'm personally not a big fan of flushing machines. In the real world there's too much opportunity to introduce contamination from dirty line connectors (machine-side), and dirt/rust/debris on the vehicle side.
If a guy just looked at some exchange machines' hose end connectors as they sit in the shop, ...and I have looked at a few, it would keep me from wanting it put on my truck. Plus it doesn't change the filter. In an ideal world a tech would clean the ends with a clean brush in solvent or gasoline and ensure they were 100% clean and not a "single" speck of dirt, sand or rust on them. And the same on the truck-side. But they don't. You might have 5 guys using the machine. The ends are often gobbed up with a grease/dirt mix, and the truck-side can be dirty too.
And how clean is the inside of the flushing machine's new-oil tank? They probably have a screen/filter, but still?? Have they mixed oils in the past? Did one worker who couldn't pass a THC test, screw up and put motor oil in a few days ago? Or type F that the parts store mistakenly delivered ...and nobody noticed, or didn't care to say anything? Overall, I wouldn't let a high-schooler or even an advanced tech put a flush machine on my truck. Unless I observed the whole procedure. The reason most trannys can "typically" last so many miles these days is they seal them up better, and cut out people from putting in whatever fluid they have on-hand and crud falling inside. And better fluid. Just a theory
I had a chance to get a tranny flushing machine real cheap. From a repair shop. Looked it over. Not too bad on the outside. It was kind of disgusting everywhere else. I'm thinking to myself, "Wow, I wonder how many tranny flushes have been done with this dirty machine?! I told myself the 'old fashioned way' was a lot more hermetic although more effort. But still, I didn't want to 'murder' anyone's transmission (or mine).
All that said, some guys are finicky with cleanliness. Hopefully the tech doing the OP's truck was super careful and detail-oriented and had everything clean when doing the job.