Mp- I use lock-out dies. They are harder to set up. (some fellas seem to never get the hang of it) I like the lock-out die better because what I want the die to do is, do the detecting for me. With some of the others, you still have to visualy look at the rod on the die to make sure it's in spec. With the lock-out die, too much or too little powder will lock the press up and prevent it from functioning until you correct the problem. Visual inspection is ok if you want to go slow and easy. But up until a year or two ago. I was shooting enough rounds per week that I needed the speed that the 650 was built to deliver. With 45acp and 9mm. I never look at a charge any longer. In hundreds of thousands of loads in those two calibers. I have never had the lock-out die fail me. BUT- you must get it set up correctly. And then you have to trust the die and yourself.
I started reloading before a powder check die was available. My high volume loading machine is a Dillon 1050. I don't worry about the powder, because I trust my powder measures and use powders that meter well and are extremely consistent. The only time I have had a problem is when the powder measure broke. I found the problem after loading about 85 rounds, so I couldn't tell exactly how many rounds were made without powder. I ended up pulling all the bullets, and it turned out 5 did not have powder. Yes, this was a PITA, but anything mechanical can fail, so I must say that even a powder lock out die may fail.
When I load my self defense ammo, I use my Dillon 550 and visually inspect each case for powder. It helps that the +P+ loads I use fill the case pretty high so it is very easy to check for powder.
I have reloaded well over a quarter million rounds in my shooting career, and can only think of two instances that caused problems, and these problems were due to breakages of the powder measure parts. Dillon replaced the parts for free. I am sure a powder check die is good insurance, but I am so in tune with my reloading machines, I can feel a problem when I crank the handle. I guess you can call it good situational awareness. When I am reloading 9mm cases, an easy pull of the handle usually means I accidently resized a .380 case that got mixed up in the brass. A hard pull of the handle may mean I just flared a .38super case that got mixed up with the 9mm. Most all high volume reloaders do the same....they get to know and feel their machines to adjust for minor problems.