"Fixed" bias versus "auto-biasing"

Thanks to both Kehut and Banksfriend for your responses. I appreciate the input. Can either or both of you tell me briefly about tube replacement when the amp is auto-biasing. That is, I assume that a single tube could be replaced if necessary rather than having to replace a pair or a set of four? With an auto-bias amp, is it even necessary to purchase "matched" tubes should one tube only go bad? What kind of tube-life should someone expect, generally, or is tube degradation something I'd recognize without much trouble?

Again, this kind of info has meaning for me. Over the past 7 years I've gone from two different Classé amps to two different Pass amps to, this past year, a Pathos Classic One/Shanling SACD (tubed output) combination. I want to slip into tubed amps/preamps, so I'm starting with an Almarro A205A, but I'm currently using a small Sophia Baby amp until the Almarro gets here. Cain&Cain speakers (95 dB). I realize that quality will be defined to some great degree by dollars invested, but the Sophia makes it clear to me that I'm going to enjoy tubed gear and I have greater expectations from the Almarro. Neither amp is expensive, of course, but I'm thinking I'll find what works for me without having to fork out too many dollars (PrimaLuna seems to get lots of good press, though Almarro does, also). I don't really want to spend more than $2k nor have something that could warm my entire house.

All of my questions simply reflect some underlying doubts or concerns about tubed amps ... I guess I've always sensed that they might just be one ongoing headache ... tubes burning out, noisy interference, way too hot, too fragile, etc. I think I was greatly misinformed.