I fail to see how this method would be better than the double-slit one for piercing aquifers, given all the extra construction needed to isolate the output tile after building a track stop on it, unless I've missed some clever twist.
However, it sounds quite useful for dealing with open fluids, where you otherwise run the risk of killing your pumper by sweeping it into the drink. With a sufficiently large array you might actually be able to do construction in the magma sea with limited risk to the dorfs involved (the pumps would be powered to avoid unfortunate accidents when a pumper tires, of course).
I messed about with aquifers and these dwarven sinkholes. I did not find the portable drain very useful for that task. However, using it to pierce a volcano safely and at any depth is super handy. I in the process of casting a huge block of obsidian... Inside the shaft. Because I want to mine out my lava submarine, not construct it... Can't engrave constructions. Also want to know if such a fort would be considered inside.
The whole thing will submerge, once I stop draining the magma down a portable hole.
You can constructing buildings in that pumps intake channel, you know? All while z levels of magma hover over your dwarven builders. A grate makes sense, or a floodgate, but what about a roller? Put another PD there and seal off the opening, and you've permanently lowered the level off magma in the shaft.
Also makes fluid traps wayyyy easier to set up and manage.
And my plumbing system just got way more compact... no more draining off the edge of the map, or into the caverns for me.
Finally, just for giggles, consider a minecart loaded with water on a track stop dumping into a wall. Can you fill that hole with magma when the track stop is switched off, not dumping?
What happens when you switch the stop on?
I'm gonna find out.