I bought the PS4 Killzone Bundle from Amazon. It also comes with a 1 year membership to PS+. I am already a member of PS+. If I redeem this voucher will the monthly charge for PS+ be suspended for a year?
There is no monthly charge. There are 3 month memberships and 1 year memberships. If/when you redeem that code it will add 1 year to your current membership or renew your membership for a year if you let your current one expire.