Well I will say this thing does suck up a lot of resources, and took a rather long time for my 7 dwarves to put together (though I'm sure a well staffed fortress could probably get it together in a season, I'm sure.) You're going to need lots of iron (I think it's 3 bars per pipe section, 1 bar per corkscrew) and lots of bauxite of course. And as previously mentioned *LOTS* of power. If you don't have running water it's going to be rough even with fully powered windmills. Just powering a 10x3 area will suck up 200 power plus whatever is eaten up by gear assemblies and axles.
Also, for setup, I found it works best if the whole area is covered in 4/7 magma. This is enough so that the magma can easily be scooped up by the pumps, while at the same time can come rushing through pretty quickly when the pumps are turned off.
But it is definitely worth the cost as you laugh maniacally when you pull the lever and waves of magma come crashing down on anything in the path. And I can't help but think the pale look on the elven faces as they walk through it, realizing just how combustible everything they have is.
I can think of some tweaks for version 2.0 already.
First is to isolate the contraption with flood gates on both sides, separating the ramps from the flowing magma. Since you can't put a bridge under a ramp to make it fall away, you get stuck with a 1 deep puddle of hot death at the entrance way with the current model.
Second, if you're interested in getting the fourth source of iron, I'd put a 2 z-level drop between the bridges and the lava retention, with staggered iron bars or bauxite grates that magma can pour through, but goblin metal armor can get caught in, something like this:
--- Bridge
# # 1st Z-level below
-#- 2nd z-level below
- = solid floor
# = grate
A gap between them on the 1st level allows the magma to fall through to the level below. Then once the trap is reset some haulers can go inside and grab the gobbo armor for melting
A third idea I had was to attach a pressure plate into the corner far away from the intake pumps so when the magma gets low enough, the intake pumps are automatically turned on. This way you don't have to keep an eye on the thing, making sure you haven't lost too much magma from evaporation.
And last, but not least, create a horribly complicated mechanism so you pull one lever, that starts some water flow system that first closes the flood gates, then after a short pause cuts power to the pumps. Pause a short while, starts pumps up again, opens up bridge, closes bridge, then opens up the floodgates. If you can make a water system mechanism that can do that, you win a free cookie! (otherwise, you need 3 levers to run the whole thing, and be careful not to open up the bridge while you have the pumps off, or your supply of lava will all drain away!)