I'm no math whiz, but I think the 25USED code works out cheaper than B2G1FREE.
Example (all PS3):
RDR: $49.99
25USED: -$12.50
MW2: $39.99
25USED: -$10.00
MW1: $27.99
25USED: -$7.00
TOTAL BEFORE: $117.97
TOTAL AFTER: $88.47
VERSUS:
RDR: $49.99
MW2: $39.99
MW1: $27.99 (Free if B2G1FREE used)...