Just moved to TalkTalk from Plusnet after 4 years. It was the issue with the Inflation + 3.9% per anum price increases for me.
However....
I have been throttled since it was installed. They had always refused to accept that stating "we do not throttle customers" "That's the best your line can do" (I had 74Mbs with BT) and you exceed your guaranteed speed" My connected speed was always 54-57 Mbs, Popped on the TalkTalk router after cutover. 65Mbs off the bat.
Also, I have been lulled into appalling CS from Plusnet.
I have an issue with the landline cutover, so I contacted TalkTalk via chat from my account page. I was chatting to CS and then the technical team within 10 mins. Was added to the vulnerable list, reassured and given an Openreach appointment for first thing Monday morning and a call forward within 40 mins.
I know from really painful experiences with Plusnet that I would have still been in a queue...
I think any advantage Plusnet had with fixed price contract's has now gone since their BT overlords have aligned the price structure to theirs to include the annual price increases.