The intonation was very decent. I had the stock hard-rubber Leblanc mouthpiece.
The major problem I had was that the lower brace on the horn (I wanna call it bell-to-body, but it's the brace that connects the lower "joint" to the joint that goes down to low C -- the pictures I've seen of the newer Leblancs have more braces and in different places) kept breaking. It broke three or four times in the year I had it (and was broken when I got it) -- and I'm easy on my instruments. When it was intact, the horn played pretty decent. When it was broken, it was ... challenging to impossible. The Bb to C "break" was also a bit difficult even when the brace was fixed.
Hey, I played EXTREME altissimo on the horn (OK, I only knew fingerings up to F#) for kicks. Yes, the high notes were a bit challenging to play in decent tune. I hear there are some false fingerings that might be more suitable, but I don't think there's much need to worry about it. I do find it somewhat amusing that it's easier for me to hit the altissimo on CB or bass clarinet than on a Bb or Eb soprano.
The amusing thing is that the FASTER you play, the more unstable the horn is. Remember, I'm 6'1" and have been since jr. high. I had to crank that stand (peg) to the top and it wiggled a LOT if my fingers were flyin'. I think the 3rd clarinet players were afraid I'd kill 'em all during the end of "A Christmas Festival" or Holst's "Folk Song Suite".
It was enjoyable to play. The bass sax had a more powerful and louder sound, but the CB clarinet had MUCH better intonation and had a sound that, well, filled the room and insinuated itself into your consciousness. But it was a sound to FEEL more than hear.
I actually didn't care for the low C. I found the additional keywork cumbersome, especially considering I rarely used it.
I think you're going to do well with the horn. I was a somewhat better than average bari player when I switched to the CB and had only played the bari for about 3 years, so it's not like I had overwhelming lung power.