Ah yes, that’s an interesting question! The extra key certainly has the potential to make some of our phrases using Eb/Ab more fluid. There is also a downside that the instrument is slightly heavier. True, it’s only a small difference, but after hours of playing I think your right thumb might notice! My thoughts are this- all the past and modern day masters (as far as I can remember)- did not use clarinets with the extra key, and they didn’t seem to have any problem getting around the instrument! At the end of the day- if it works for you, then great!