I believe the Leicester Cathedral Harmonics IV (17-19-21-22) was replaced with a quint mixture (19-22-26-29) in 1972. I partly agree that the new English style Trumpets of 1998 do not have much impact but they certainly blend. I played the organ reasonably frequently when I was a pupil at Leicester Grammar School in the 1980s which was then next door to the cathedral. I rather liked the Trombas and their ultra-smooth tone - they had character. The Quint mixture is more versatile but it would have been beneficial to have had both mixtures.
At St Mary Redcliffe where the organ is now nearing the completion of its restoration by H&H, there are two mixtures on the great. This organ is from 1912, so Arthur Harrison after his Ely/Dixon experience was perhaps not immediately converted to having both mixtures? Our quint mixture (12-15-19-22-26) was only added in 1974 at the request of the organist Garth Benson (along with pedal upperwork too). This mixture has now been included on the main slider chest with improved chorus effect - it stood out a little previously on its separate chest which was at a higher level than the other fluework.
The Harmonics IV (17-19-21-22) with only one break at F#43 to 8-10-12-15 can be used in a number of ways. It can be occasionally used as a piquant reedy cornet colour with 8 and 4 flutes; it can be used as an alternative or additional mixture with the flues, and it adds sparkle to the Trombas (16, 8, 4 - separate ranks - all with a slightly different tonal spectrum). Since cleaning, and the integration of the quint mixture, the mixtures have perhaps changed roles. Formerly, the harmonics was added in hymn playing as the first mixture and then the quint second as a brighter/sharper sound. Now it appears that the harmonics might be better coming on after the quint mixture, perhaps even with the reeds as it may have originally been designated! I like the Harmonics and find it anything but useless if voiced well and in a sympathetic acoustic.