Wouldn’t jump too far ahead with this if you’re new to Matched Betting as Betfair trading software is somewhat more advanced. However, as L0U has already suggested there, the Geeks Toy is the most used and at one of the lowest prices.
Gruss is not too bad if you want automation although it would be my second choice.
Don’t forget that the site has Exchange integration (see the courses section) as standard so you wouldn’t really need it for placing your lay bets directly into the exchange anyway!
Cheers,
Caan