If I were you I would demand/request a 2nd generation smart meter. The problem with them is that if you get an older first gen smart meter, they are only compatible with the specific energy firm. Which means if you want to switch to an alternative supplier a year down the road, for example, the smart meter will no longer be fit for purpose (by that I mean, they will no longer be "smart", it will return to old style functionality) and if the next deal with a different supplier also requires a smart meter, theoretically you could be getting new smart meters every time you switch supplier. Apparently the 2nd gen smart meters are compatible with all suppliers so you should be fine.
Two helpful articles below.
https://www.which.co.uk/reviews/smart-m ... -installed
https://www.telegraph.co.uk/bills-and-u ... ut-stalls/
If you're within 14 days of signing up to the new tariff, you might be able to get out of it.