How bad is it to have zero backflow protector on Well water?

Title basically says it all. I’m a newish homeowner and we had a tech come out to turn on our system for the first time. It’s almost 20 years old apparently as one of the zones is under a deck that got built 5+ years ago.

Anyways my one question for the tech was where is my backflow protector/ check valve since I read that’s one of the most important things and I couldn’t find one anywhere. He confirmed that nope there is not one inside or out. The plumbing was done pretty stupidly as well, the irrigation pulls from the same line where my small taste filter for the entire house is.

The house sits on a hill and the irrigation is substantially lower than where the water comes in. I don’t think this matters a ton but it would be quite a lot of hydrostatic pressure to overcome for the water to back flow. My question is how dangerous is it for me to ignore this? We’ve spent a lot of money already on things like radon, fixing doors, mold etc so we aren’t exactly looking for new things to fix.