You're reducing your payout and reducing your risk, which effectively turns a $1.14 bet into a $1.05 bet (or whatever, depending on how aggressively you're laying off), but you're only going to make a long-term profit if there is some kind of market inefficiency on the U/4.5 goals markets. It's hard to see how you beat the Betfair commission without any edge.
I think there is definately a market inefficiency with live betting. I my opinion the market overreacts to small events within a game.
We see this most prominantly with the Big Bash. A player will hit two sixes and the odds will go from $1.80 to $1.50 in two balls. Same when a wicket falls. The change in price is more than it should be in my view.
Anyway, it's all a bit of an experiment. I'll let you know how it goes. I think we should all be helping each other out on this board.