IMO, it's far easier to make a mistake and under or double charge with a single stage press than with something like the Dillon. I'd really have to go out of my way to do that on my 550.
Lots of folks will disagree particularly with the manual index Dillon 550.
Bottom line is one needs to check and double check the powder charges to make sure there is not a missed charge or a double charge.
For single stage work, I batch charge a tray of cases then look in each one before moving on to the next step.
For progressives, some folks look in each case, others have some kind of powder check system.
I did not have a squib load for close to 30 years of reloading until I added a progressive press to my reloading room three years ago. I have since altered my reloading process to prevent charge problems in the future.