@Mat74UK not just impractical, impossible. Right now it’s even theoretically impossible, but it could theoretically become theoretically possible someday, which is the first step to eventually becoming practical too.
First of all, the spaceship would be stretched and crushed and obliterated (thousands of miles before it even entered the first black hole). I mean these things bend light, what do you think they’d do to your cockpit? Or your spine for that matter?
Secondly, the instability means that the wormhole would probably not be there long, and could disappear while you’re in it. What you said basically. To use jackm’s example with the needle, a wormhole is like balancing two needles on top of each other, and then trying to persuade an ant to walk up to the top without falling off.
Thirdly, we have no idea of knowing where the second blackhole leads to, since we can’t even send an electromagnetic signal through it to find out anything about the exit. It would by definition be a one-way journey, possibly even to another time-space continuum altogether. Or even to a parallel universe, who’s to say?