I had a Low C extension put on my upright with the Fixed E Latch...
I love the Low C (and other notes) when I do use it.
But I mainly keep it latched.
(I mainly play Jazz on it)
One thing I do miss is for example, when walkin a bass line in C, hitting the C on the A string and then the anticipated open E string looses its impact with the fixed E. Even when I tighten it all the way, the open E doesnt have that large tone that basses without extensions have.
If I knew it was going to be like that I would not have put on my extension.