Danny, I also water based mostly on weight now, although I don't do it nearly as accurately as you do. I agree 100% that it greatly decreases overwatering to do it that way. I agree that the water weighs about as much as the pot + mix + cutting, so that's why it goes from 300+- grams bone dry to 600+- grams nice and moist. Since that's a pretty wide range, I just lift it up and if it feels light, I water. Also can sometimes see little droplets on the inside of the cup, that will give you some info as well.
I think it's also important to have a fine potting mix that will wick water efficiently. Should be pressed in the cup somewhat, not just left loose. If it doesn't wick water it would be possible to have too much moisture at the bottom or top while being dry elsewhere. If wick action is working effectively, moisture level will be fairly uniform throughout the majority of the cup. For this reason I wouldn't use pine bark fines for rooting indoors, since they might not wick.
Also, if you have mix that wicks, if you ever accidentally over-water, you could correct the situation by rolling up a paper towel (some good stuff, like bounty) and pushing it into the bottom of the cup, then ensuring this towel is firmly touching something outside of the cup that will absorb moisture, such as a towel. Then turn on a fan to blow on it. You get the idea. The excess water will wick away over a few hours.