Is there such a thing as a good Strida clone? What are the qualitative differences between any clones and a real Strida?
From your comments, it sounds like you're hoping to find a folding bike that folds up fast, but is also light enough to carry up stairs easily and small enough to fit through turnstiles and on the train with no problems. All for well under $1000.
This may be impossible. There are cheap folding bikes (under $500) and there are lightweight ones that fold up small and easy to walk around with. You might be able to find something that meets all those criteria for cheap that's used, but I don't think you can manage that with a new bike.
There is the A-Bike which is quite similar looking, but has a different folding mechanism.
There's plenty of competition for folding bikes out there:
The big problem with any bicycle with such small wheels is that the ride is going to be rough and it'll be easier for the wheel to get caught on something instead of rolling over it; most compensate with wider wheels and tires which should help eliminate some of the roughness. Depending on the folding mechanism there's potentially structural (strength) problems with folding bicycles, though many compensate for those with additional material and instead make the bike heavier.
Personally, I'd see if there was someplace I could give some folding bicycles a test ride. I'd be likely to go with something with 20" wheels instead of 16", too. 16" does fold up smaller, but 20" is pretty close and should be a much nicer ride.
I've commuted by bus + 12 km Strida every workday for about a year and a half now.
Before my purchase, I researched the folding market thoroughly, and came to the conclusion that Strida was by far the best option. I've never regretted that decision, and even bought a Strida for my wife for casual riding (found one new on dba.dk for 2.250 DKK) due to my fascination for the bike.
I must add that besides the quickest possible folding/unfolding time, my requirements also included that the bike should endure being outside during office hours, and the harsh Scandinavian winter (I live in Malmö, but work in Copenhagen) is not kind to bicycles.
The Strida differs in that respect since basically everything is made of aluminum with a front pulley made of plastic and a belt drive.
Soon two winters have passed, and everything is as good as new! Marvelous! Oh, and the bus company really like the grease-free belt drive!
One of my fellow commuters fell in love with the bike, but wasn't sure, so he bought a Chinese fake Strida off of the German ebay. The frame broke after two months!
My advice to you is to look for a used Strida (preferably a v.5+ model with rear aluminum pulley) instead of buying a new lesser bike.
I had an earlier version of the downtube about 5yrears ago.
Mixed feelings, it has some nice features - folding pedals, nice chain guard, comfortable position and a bit of suspension to make up for the small wheels.
Component quality left a bit to be desired, a nine speed no-name rear with friction twist grips to select! It folds - but only in a store under the stairs sense - if you need something that collapses into your pocket, get a Brompton.
ps. When they used to sell on ebay and with a favorable exchange rate I paid around $250