I haven't played the conklin, but from what i've heard it's the best for the price. I play around with the 7, but i would never gig with it, for fear of making myself look like an idiot :]
Mainly, i play with chords on it, and use it for jams with bass player friends... I'm considering selling it, simply because I know a few people who could put it to much better use than I do. It is fun, though, i must admit. The neck isn't as huge as one would think, it's actually pretty comfortable, and the thing sounds beautiful up and down the neck.
The one thing i can say about 7-strings, is that if you like playing in the higher octave, or use Piccolo basses (which i do), and dont like having to switch basses frequently, I would suggest getting a 7. It actually has a higher range than a piccolo, and you still have enough low end to shake the house.
It's definitely worth the investment if you think it's something you'd really put to use.
I hate to admit it, but i just thought it was pretty :]
Take it easy, hb.