If I could choose my carvin again, I'd have gotten lines on it.
You can't hear if it's out of tune before you play the note. If you're about to start a note that has no reference point on the instrument, you CAN'T guarantee it's in tune simply by looking at the side markers, specially when on stage playing on the G string with the neck or your hand at an angle. Playing fast? Jumping around the board? You WILL eventually miss. I've played violin my entire life. You can play it very accurately (although sometimes still make mistakes) due to the feel of the hand position. You don't get that feel on an electric bass. There is virtually no feel at all that tells you when you are firmly in a known higher position, at least not until you hit the neck joint (which is way too high to be useful for most music).
Fretless with lined was how I made my career successful back in the day, and even though you don't need to look most of the time, when you have that big shift or jump coming up, or you want to solo, you'll really appreciate knowing where the hell your hand is BEFORE you hear that you missed or were out of tune.
There are those who say that isn't true if you practice enough.
I'm absolutely not saying that I'm as good as the great players out there. BUT, I do have 2 degrees in music performance and made a serious living playing full time on electric bass, fretless mostly, and on violin, for a long time. I'm not lacking anything in talent or ability to hear pitch, and I've performed some huge legendary works on violin, so I know how to practice.
But the bass guitar has a long neck with virtually no feel to where you are on it aside from large motor skills like your bicep and similar muscles, which are known to be inaccurate at exact location repeatability.
So don't deny physics, and don't pretend it's not true. You might be able to play great on unlined (I play unlined these days). But you can avoid a money-costing (or rehire-costing) booboo with fret lines. And yes you can look down at the front of the fingerboard if you need to... it's pretty easy actually.
Just my personal suggestion from my personal experiences. From a guy who plays unlined LoL.