Having experienced plusnet traffic management before,I wouldn't want to try plusnet again without the option of a 1 month contract. It can be nasty but particularly stupid when it assumes something on a non-standard port is peer-to-peer.
For a long time all Plusnet(ADSLx) packages have been monthly contract on 10 days notice. The 12-month contract is worded deceptively, but in reality all it means is that people wishing to leave early merely have to pay the setup charge; for the router if taken; or house move charges if they have moved for free within 12 months.
On the Fibre option I expect there will be a genuine 12-month minimum as that is what Plusnet have to contract for with Openreach.