Basic info: I've owned an LB70P fretless, LB75 (2 jazz pickups), BB70P, BB75, and a Bolt guitar.
The good -
- They build what you want them to build
- They can be purchased for little on the used market
The bad -
- Underwhelming electronics
- Necks require frequent adjustments
- They can be sold for little on the used market
Just to elaborate further on the positive. The feel of their instruments is on-par with American Fender instruments. Considering the sheer number of options (with the exception of electronics), you really could build an ideal instrument.
Now, as for the negative aspects... Like I mentioned above, I have owned quite a few Carvin products. Some people like the electronics, others do not. I happen to fall on the side that really cannot stand'em. Terms like "thin," and "lifeless" immediately spring to mind. You cannot get the Music Man tone. You cannot get the Jazz tone. What you get is a very bland, vanilla tone. Sure, it's serviceable, but when you trick out woods and get an electronics system that negates the inherent tonal qualities you would expect from ash, or mahogany, it just plain sucks.
After swapping the J/MM setup on the LB70P to Nordstrand single coil and vintage Sting Ray pickups, the bass sounded a heck of a lot better. Like "night and day."
As for their necks... I also have found their necks to be quite temperamental. Every instrument I have owned from Carvin required constant attention. Lower the action one day and its great. Come back the neck and you have horrible buzzing. It really got on my nerves.
For what its worth, I do like the build quality of Carvin instruments, and at their used price point, they make great choices for backup instruments, or instruments to keep around. I do not think I could go back to their stuff though.
Just a final note... the Icon series is pretty nice. I had a chance to mess with a few Icons at their shop in Cali. I was STILL a little disappointed with the electronics. Still too pedestrian for me.