BT Black Friday (2020) 'Free Upgrade' Deal

SMOTP

As a BT customer we have been offered a 'FREE' upgrade to Halo2. It says "it takes reliability and service to the next level – with loads of extra benefits exclusive to BT Halo 2 customers. But don’t wait around, this offer ends 3 December.
It asks "So why wouldn't you?" 
It seems too good to be true... and often these things are.  
So MSE, why shouldn't I?   
The small print says: "Our Price Promise: You'll keep the same monthly price, when your contract ends. This doesn't include any changes as a result of annual percentage increase in the Consumer Price Index (CPI) rate of inflation plus 3.9%. See bt.com/prices for more information."

Yahoo_Mail

Did your contract start before Sep 2020?  If it did then the catch will be that your annual price increase which is currently CPI, will become CPI + 3.9%

EssexExile

I noticed that in the earlier versions of this promo it said "for £5 less than you are paying now". I went on various forums and found that as you went through the ordering process it became clear that this was not true. Now it says "for the same price" but as there is nothing in Halo2 that I need I will give it a miss.