Auto-bias and protective features are mostly there for marketing. More and more people are coming around to the superiority of tubes. But tubes carry the stigma of unreliability, even though as you can see from the comments here they can be just as reliable as anything else.
To put the protective circuit thing in perspective, tubes have been used for more than a hundred years. They may be new to new customers, but believe me they are not new to tube amp designers. They have like a hundred years experience designing amps to survive blown tubes. Protective circuitry in other words does not have to be anything added. It is just plain good design. Which is why I say for them to draw attention to this is pure marketing.
Auto-bias, same thing. I’ve had amps that had this and amps that didn’t. The amps that had manual bias I have stayed on top of- except for when I didn’t. Times I wanted things to sound really good spend extra time getting bias absolutely perfect. Cannot honestly say I ever heard any difference due to bias, not even the one time I found it had drifted way off. More marketing.
Tubes on the other hand, yes there are differences and yes they wear out and yes it is best to replace the full set. Although again, not that I have noticed any problems. From the beginning when a set was replaced I would keep the old ones around as spares. You definitely want to do this. So when a tube goes bad oh well pop in a spare.
Tubes can go bad in anywhere from an hour to a decade. There are basically two ways they go, the supernova and the slow fade. The supernova is really cool if you see it, blue light storm in a bottle, red hot melting, makes you understand why tube sockets are ceramic. The slow fade they get softer and mellower very very slow and so gradual so it can be hard even to notice. Until you pop in a fresh set and, wow!
Haven’t heard PL, but I do a ton of research before deciding and my short list is Decware, Raven, Audio Hungary, and PL, in pretty much that order. Although honestly you cannot go wrong with any of these. Someone mentioned the Kevin Deal breakdown video. I say breakdown because the man is clearly having one. Courtesy, Raven Audio. Sad. So sad. But he did get one thing right, they all sound good. It is kind of like turntables. Another one where it is almost impossible to go wrong. I’m real happy with my Blackhawk, and have my name on the list for a Decware ZMA. But I’m sure you’ll be fine with PL.