I am new to fretless, but certainly loving it (Bongo though, not SR5).
Ordinarily I tend to play agressively, with ample fret "snap" - I like the fretless for the softer, melodic stuff. Stuff that moans...

I find I am in a different mental place when playing the fretless.
Piezo is HUGE (sorry Chuck!). It definitely adds a unique edge to the tone - sensual is a great way to put it.
I considered both lined and unlined and ultimately went without and glad I did - for me it's all about the side markers...
The lined neck is marked along the side just the same as a fretted neck. That is to say the third fret side marker is between the second and third line.
Using the 'A' string for example, I look for that dot to play a 'C' on a fretted neck and the fret does the rest. But on a lined fretless, playing the dot is flat - the 'C' is ahead of the dot on the line where the fret would be. On the other hand, playing the 'C' on the unlined fretless is right on the dot as the side markers are where the frets would be.
This is HUGE for me, as it means I can essentially use the same approach for both the fretted and fretless necks. And while I certainly have some "tightening up" to do with regard to my fretless playing, this has made playing the fretless bass much easier for me that I expected.
Go for it Chuck - fretless is cool!
