If you buy Smash normally it's $59.99.
If you buy SMM2 normally it's $59.99.
So yo'u've just spent $119.98.
If you buy the voucher pair it costs $99.99.
You redeem one voucher for Smash.
You redeem the second voucher for SMM2.
The difference between $119.98 and $99.99 is the saving.