Keep your cash.
A flea "bomb" is simply a can of insecticide that sprays by itself. You start it, set it down, and get out of the room. I suppose that is how the term "bomb" was coined but aside from your bank account, nothing blows up.
There are a couple major problems with flea bombs. First, they are toxic and you'll be coating every square inch of your house with poison. Common sense tells us that that is a bad idea. Second, they don't kill the eggs. This is why people use them over and over and over again to no avail and I think this is one reason why people think that fleas are virtually indestructible. They aren't but the eggs are.
It is my opinion that flea bombs are a dangerous waste of money.