When they work, they're quite beautiful! As well as the buss, track and group metering, there's also a 'spectra' which makes the whole meterbridge a spectrum analyser... very pretty.
However, the tubes go bad unfortunately, and are no longer made. -They were actually SHAVED DOWN slightly, to fit in between the LED scale backlighting, so most replacements don't even fit physically.
In addition, the logic can cause some grief, and the high voltage 'MPSA'-series transistors can break down over time also, which tends to make little dancing traces appear, and sometimes makes the whole bar light up at all times, dramatically quickening the burnout of the tube.
On top of that, troubleshooting REGULARLY causes 'nips' to the servicing engineer, because the whole thing runs on 250VDC inside the meter bridge and across the whole of the back of the console... The number of times that clients hear that little "spit" followed by some inventive curse words, and a "bang" as the rapidly-withdrawn elbow bangs into some unyielding part of the heavy cast metal frame.... well, I think that any tech who's ever had to work on those things will smile a wry prayer of thanks that they're not doing exactly that right now!
Keith