I have tuned probably 15-20 13B turbo engines, up to 700whp on street driven cars - for some reason where I live they are very popular. A friend of mine rebuilt one on his kitchen table - they go together like a Ham and Cheese Sandwich - in about 45 minutes.
I know that in the past 5-10 years the aftermarket has really sorted out the Apex seals. Another surprise is how popular they have become in homebuilt aircraft. Lots of guys are flying N/A and turbo 13Bs now.
I just recently tuned my first 20B, a three-rotor engine with a large single turbo, capable of an easy 1200whp if the rest of the powertrain can handle it. Pretty impressive really.
Another strange thing I learned about them, some people get "motion sickness" when they are around these engines at WOT. I have no idea what the reason is, but I know a number of guys who just cannot be nearby when we are running them on the dyno - they get queasy. I know one guy who had to quit his job on a drag team because every time they ran the car - he got sick.
They are not really that fragile anymore, I heard one detonating like mad on a dyno pull, I was told "one hint of detonation and they're done" but I don't think that's always the case - this one was rattling like a tin can full of marbles, until we sorted out his ignition and fuel.
They are fun engines to tune, easy and rewarding when you lean on them with lots of boost.
Custom EFI setup and calibration