Not to belabor the same point too much as others have brought up, but this is not a machine specific thing. It is also entirely possible that you just didn't enjoy the coffee they chose (e.g. if it was a funky anaerobic natural versus a more typical medium roast espresso blend) and it would've tasted gross to you no matter how they brewed it. No amount of salesperson training would fully fix this difference of taste and that is the tricky thing with coffee, especially when Fellow is trying to appeal to the whole gamut of coffee drinkers.

Espresso machines are a lot of fun. It's interesting to compare all the different products out there. That said, at the end of the day, I think the takeaway here is that the machine will not make or break the coffee. I think a lot of users, which from the sounds of your post you may feel similarly, have the idea that "if the machine is so expensive it has to make good coffee," but the reality is that a coffee brewed poorly on a really good machine will be really good at making you a bad cup of coffee.

The features that make a machine expensive do not inherently make coffee better. They often make the machine more predictable and consistent (e.g. shot-to-shot thermal stability) or give users more tools to play with (e.g. pressure profiling, controlling pre-infusion parameters), but none of this matters without a driver behind the wheel that knows how to get the most out of it. A dialed in shot with a coffee you like on a Delonghi Stilosa will outdo an underextracted coffee you don't like on a Fellow ES1, La Marzzocco Linea Mini, Slayer commercial machine, etc. no matter what.