I checked this back 6 months in Neale Yardley's Bet Selector program and got these figures
races 477
bets 522
longest lay collect run 32
average payout odds using NSW tab odds 3.73
showing -50.6% when win backed on NSW tab.

would need to be checked using actual Betfair lay odds of course
but looks very good.
I presume this is a win lay method not a place lay method?