I assume you aren't hoping to transfer your phone number to the new premises. In which case having a line installed by Sky or TalkTalk probably means you will be given a number from their pool.
AIUI that can cause some (not all) CPs a problem if you later wish to migrate to a BT Wholesale based service.
Other than that, as Ian says.
(As an aside, technically there is no such thing as LLU on FTTC, but we know what you mean. LLU refers to the CP completely controlling your line settings at the exchange and your line entering the exchange connecting directly to their DSLAM/MSAN. On FTTC the DSLAM is Openreach's and is in the cabinet, with Openreach offering the ISP a few stability options and such).
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