We were recently discussing these, so I figured I'd get one and do some tests. It looks suitable for switching high currents at voltages used in O-gauge equipment, but it's not perfect.
Lightly loaded with a fairly low drive current in the 1-2 A range, it drops about 2.2-2.4 VAC across the relay. However, if you crank up the current to 6A, the voltage drop is only around 1.6 VAC. I also noticed a higher input voltage at lower currents seems to minimize the voltage drop. At 16 volts and 2A current draw, I was getting around 1.7 VAC drop across the relay. As long as you have some headroom in your AC power voltage, this is a good solution for switching AC voltage to accessories or track power districts. They are actually specified for 24-380 VAC, so running them at typical O-gauge voltages is below the minimum rating, but it seemed to function just fine.
The input signal requirements are pretty broad, 3-32 volts DC. I measured about 12ma input switching current, though their specifications claim 7.5ma at 12VDC.
This is the relay in question, they're available on eBay for $3-4, I bought the one for $3.25 shipped, I ordered 5 more for $18.55 shipped.
