I've heard of the block issue, but never experienced any issue.
Gramps ran 4 ZWs (and a fith hot rodded to #1 for running ABBBA-7 motors and up to 24 lit cars... but I was too young to learn how to do that ) I had a KW that II used (& phased.. important with two!) with all kinds of smaller units. Today Ive done similar with pre war Z running 4 blocks, a KW on a fith block. No issues so far over about 6 years.
I'd fuse your outputs or use an electromagnetic breaker on each. Current being amps, a fuse or lower amp inline breaker limits the max amps that can pass. A ZW can push up to 15amp to one throttle for a count to ten! (you can just about weld with it)
You likely wont use that. A 7a-9a peak (not even a constant) is more like it on one throttle, with your largest 2 motor loco pulling lit pass. cars. Measure your draw and fuse accordingly, keeping it as low as you can without blowing is prudent.
(Lionel made one post war, I don't recall the number, but search with "electromagnetic breaker" and look for posts by CW.)
The internal breakers protect the TRANSFORMER, not the track, accessories, trains, kids etc..(it does to some extent, but it's not really the goal there) Fuses and/or breakers on each line are better. No scarry current beyond what you fuse at. It simply can happen.
Another way would be track detectection before and after another isolated block..(3 total; 2 big,+ 1 transition block). The triggers pull a relay that switches which power terminal to use. When fully past a trigger, the 3rd section switches to the upcomming power input. Hard to do at times, the transition block must be long.
Come to think of it, there is one thing that these blocks can cook easily. Bulbs and even thin wire in cars with two rollers. The time of the bridge is too long. A poly-fuse to equal bulb draw is a fix. Two placed between rollers and bulbs in each such car can cure that. (a modern very fast acting, very fast self resetting fuse). Because of the reset speed, do not use these poly fuses as you would a normal fuse.
( also, some techs call breakers fuses in discussion because the two are mostly interchangeable unless you are being specific; usually for the choice; and thats usually apparent. As a verb I use "fuse" most often)
I hope This makes sense because "google-spellwreck and "vindictive text" has kept me at this lone post for near two hours..... hardly three words without it screwing up or changing a line I can't see anyamore ... like what IS "anyamore" anyhow? The features are off too 
I.e. I need a break and won't reread it before posting.
