Here are some stats from when I started in September 2015 to now.
An overall PL/TV of 0.042%.
The number of markets my bot has monitored is probably double the amount it has traded in. Also the number of bets placed will by higher than those settled as I use a fill/kill.
Something else I was thinking about is how Betfair talk about the amount of money they match in events such as the Euros etc. When you place a £10 bet it is recorded as £20 matched, so including the opposite stake. My £600K would be £1,200,000, approximately. But this is done with a bank of a couple of hundred quid. So I wonder how much actual money is used to trade the millions on horses and football every week? Probably only a small proportion of the final “matched” figure.