I wrote the reviews for both speakers and the Kanta No1 continues to live here with the kind permission of Focal;
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The Kanta is not four times as good as the LS50 Meta- it's a statement of the blindingly obvious but it warrants repeating because people tend to fall back to numbers.
Something that might also seem counter intuitive is that the Kanta is easier to drive than the KEF. It has a higher sensitivity, higher minimum impedance (and spends less time near that figure than the KEF does to its). You can (and I have) achieve very satisfying results with the Focal on a thirty watt valve amp which you can't do with the LS50 Meta.
In performance terms, the key difference between the two is tonal realism and detail retrieval. The KEF is exceptionally good for a £1,000 speaker but; used on the same partnering equipment (the Mscaler/TT2 into the Edge A mainly), the Focal will do things with voices and instrumentation that aren't really hinted at when the KEF is running. Uni-Q is exceptionally cohesive but there aren't many brands at any price that can extract more from a recording than Focal can. The reason why the Kantas are so useful for review work is because they relay exactly what the equipment further up the chain is doing.
The 'worth' of these improvements is entirely up to the purchaser but a £1,000 speaker punching above its weight won't trouble a £4,500 doing much the same thing.