Hi,
I’ve been recording the neurals for some time now and ran this thru my database from Sept 2004 to Nov 2005. I don’t have prepost prices so instead used unitab favourite.

Excluding 2yo races, there were 6794 selections for 1853 winners, 27.3% SR. The return was 5826.3 using unitab dividends for a 14.2% LOT.
The SR for all unitab favourites over the same period was 31% for a LOT of 13.4%.

So there is a significant reduction in SR but loss on turnover is similar. I would think that the difference between the unitab price and your lay price with betfair would account for the majority of the 14%.

Cheers