I'm not a bass guitarist but do occasionally play bass in a jazz trio when I'm not playing guitar or sax. I bought a Harley Benton JB40fl several years ago and am very happy with its sound, but I'm struggling with the weight so I decided to look for something lighter.
Top of my list was the Ibanez range but I had doubts about their suitability for me because their fret lines are almost invisible and I'm not sure I could deal with that, and they seem to offer a wide range of sounds for different styles of music, rather than focussing on imitating an upright bass for jazz, which is what I really want.
I discovered the Sire quite by chance on Thomann's website and decided to give it a try. It's exactly what I was looking for. As others have said, it's extremely well made and a pleasure to play so I am very happy with my decision.
When I first plugged it in I thought it was a disaster because it had a very distorted sound but I quickly discovered that was due to the pre-amp settings and that turning down the treble and mids produced a much cleaner sound. The output from the pre-amp is much louder than is needed but that is easily controlled with the volume and eq sliders. Even with the D'Addario strings the guitar gives a very good representation of an upright bass and the pre-amp gives you a wide range of tonal options. I expect the sound quality to improve further when I put on the Thomastik strings I have ordered.
Compared to my HB, overall, it is more comfortable. It is lighter which is going to be a huge help when playing sets. The neck is less chunky and more comfortable to play but the action is higher than my HB and there is limited scope for adjusting it without going to a luthier. I'm also not keen on the high gloss fretboard but it's not a big deal. As far as sound goes, they are just different beasts. The HB has a very good fretless Jazz Bass sound and the Sire is more like an upright bass.
I can highly recommend the Sire if you are looking for an upright bass sound. It's good and the price is amazing.