Uh oh, it's mighty dark inside the mouth of this alligator!
I'll start by saying I am not a fan of black box power control. I participated in the design, marketing and installation of just such a box for military aircraft applications. The comments about adding semiconductors and software to what essentially is a hardware function are right on the money. Unless there's some very specific benefit one absolutely has to have from electronic control of power switching, generally the added complexity and higher inherent cost and lower MTBF of black box power controllers makes more traditional switching and circuit protection a wiser choice.
Now I'll also say I've spent a lot of years upside down under instrument panels in everything from attack helicopters to heavy transport aircraft. From those years of experience I will share the following thoughts.
1) The capacity to confirm power settings both visually and by touch put switches and breakers MILES ahead of any black box. When the cockpit goes black dark on a moonless night, running one's fingers over the breakers and switches is a huge advantage, particularly when one is also supposed to be keeping the airplane right side up!
2) Switches and breakers DO FAIL. I've replaced enough of them to say that the combined breaker-switches tend to be the least reliable of the gang. The typical Klixon pullable breakers (7277 or similar series) are generally reliable UNLESS somebody has been trying to use the breaker as a switch. Just don't do it!!!! MS-style switches have terrific reliability. Many switches I've seen in amateur-built aircraft are not of high quality, particularly the ones which have been chosen because they feature Fast-On terminals for wire connection. Again, spend the $$ and the time to get good switches and connect your wires to the switches using AMP PIDG ring tongue terminals and screws. You can't get more reliable than this, period.
3) Since switches and breakers do fail, one important pilot skill we should all develop is the ability to detect the warning signs of impending failure. In switches we sometimes feel the switch getting "gritty" before it dies. We also feel the cam-over point changing or becoming less defined. These are signs of mechanical wear-out. Circuit breakers often become somewhat resistive before failing. Running a finger over the panel surrounding the breaker can sometimes alert you to a breaker that's running warm - if it's warm there's something wrong. If a breaker suddenly becomes easy to pull, get a new one, quick, because it's going to fail soon!
4) Never, ever use the slot-head screws that come with some Klixon breakers. Toss 'em and install Phillips head screws. You'll thank me later!
5) If you can find flexible bus cables rather than solid bus bars, use 'em. They make replacement of a failed breaker much easier. HINT: Some business jets and regional airliners which are being retired are good places to source these bus cables.
6) Almost universally, the failure of a breaker or switch effects a single system, the system for which the breaker or switch is controlling power. Failure of a "black box" power controller can (and does) effect everything it controls.
7) A local builder used Poly-fuses in his aircraft - so far they have performed flawlessly. They are tiny compared to a traditional breaker but that tiny package does make for some challenges in connecting to them and installing/isolating them in the aircraft.
8) If using automotive blade-style fuses, the LED failure indicating ones are absolutely the bees knees. They make troubleshooting almost as easy as feeling which CB has popped.
9) If there's any way you can do it, install a spare circuit breaker and wire it to a spare switch. This makes addition of any equipment, even just for a quick test, a zero-fuss affair.
A few years ago I was asked to help troubleshoot two electrical faults in the same week. Two different airplanes. Two different sets of symptoms. In both cases it was a Klixon circuit breaker which had failed. In one instance the aircraft was to dispatch the next morning for its annual pilgrimage to Oshkosh, so it had to get fixed. The CB had simply failed open-circuit even though its plunger was fully pressed into place. It took me longer to get under the panel than it did to troubleshoot the problem. I briefed the owner that I would move the wire from the dead breaker to a spare breaker and that he would have to label the spare breaker. Problem fixed in a few minutes. In the other aircraft it only took a few minutes to discover that when I put my finger on the head of the breaker's plunger the VHF radio would blink out. Hmmm, that was easy! Luckily I had a spare breaker in my toolbox - a few minutes work and then we had to perform the obligatory post-maintenance test flight. Yippee!
Now compare these break-fix experiences with some of the challenges we've read about in these forums when the black box controllers go awry. Thanks, I'll take stone-age simple any day of the week.