they do work however there is a bit more work you need to put it.
1 - yes try to make sure it's as bare of ground as possible.
2 - make sure the PH levels of the soil are good for what you're trying to grow.
3 - toss the seed out on a day you know rain is on the way(if it sits too long the birds will get it)
4 - Make sure the area you're planting in gets planty of sunlight.
These should be a good start.. I've had fairly good luck so far with no till seed.