It depends how much you want from the $50 free bet. All free bets I try to arb so I get more than $50 (for example).

Yesterday with my $500 free bets, split in to 10 single bets, about half of them I laid off on Betfair and they were arbs. The others were super close i.e. back/lay odds 10.00/9.80 etc. With bonuses, and I guess most do this, I go straight for odds 9.00+ and if I'm lucky find an arb.

From the $500 free bets yesterday I ended up clearing about $500 from it and made about $550 through normal arbing on top at night.