You mean you've tried it and it's OK?
As long as your home wiring is fine and was giving good ADSLx performance the Openreach install is probably overkill. By using the extension you are of course using relatively poor extra cable unless you had already installed Cat5/6. So the extra length could matter - VDSL2 degrades with distance more rapidly than ADSLx.
On Infinity you could have had a free "Data Extension Cable" fitted to give high quality cable all the way to the extension site, but that's history.
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