I don't know about what it would be like riding with my son, or my girlfriend (they're close in height at the moment). The only way to find out is to try, and for £70, it would've been a cheap way to find out. So, it looks like with this, it would've been a matter of a different set of pedals for the captain at least, and aluminium rims, which are easy to find, plus a service.
I'm now seriously on the hunt for a cheap and servicable tandem. Watch this space. If we can't ride it together, or it's a bad fit......well you know me. I'll make a profit on it!