Since, like every other poster on the thread, I too have no absolutely no experience of the Solorock 20", I feel qualified to weigh in
At the price I'd risk it. It doesn't look like a lemon. Not sure I'd trust it to hold up to 150 km a week commuting in all weathers year in year out, but then nobody ever used ye olde Eastern Bloc folders for that either. Today's fold better, have a lot more alloy and good brakes. You may be pleasantly surprised. Always a good winter/rain/pub/concert bike if and when you move on.
That vintage Road King, admittedly, looks quite lovely.