I think these things are a neat idea, so I got one cheap on Amazon not too long ago. I picked it up just to handle one in person, and it serves it's purpose well.
I might attach it to this old "All Pro" roadster-like bike I have kicking about as my vintage restoration project bike (hey, 70's is vintage!).
It is specifically this one:
"FengYe YuanZi" is labled on a sticker. There seems to be a couple very similar ones to this kicking about in different color schemes. They appear to be built similarly.
Now, this lock isn't great. O-lock acceptance being what it is, this one has a few unique problems. Firstly, and most importantly, the tabs that would secure the lock to the bike's seat stays only have small welds. They don't move with thumb pressure and the metal itself is fairly substantial, but none the less it's a little disconcerting. Secondly, the lock's bolt isn't very "accurate" - that is, if you just slide the handle down, the bolt tends to not want to line up perfectly with the other side, which makes it a little fiddly. Lastly, the engagement handle is a little flimsy, and wobbles within the bolt.
The keys are made of galvanized steel, and are pretty light and small. I'll have to translate the characters on it when I get a chance. The key ring is surprisingly substantial - better than ones I get in the US half the time! These can't come out of the lock unless the lock's fully closed, like other O locks dating all the way back. This is good, because the bolt can hold whatever position you slide it to, and it has a position where it looks closed but can actually just be slid back up without issue. This isn't a problem because if it's in the position you can't remove the key, which prevents any illusion.
Very neat little device, for what it is. Mine cost a whopping $12 on Amazon, and I don't think I paid for shipping, either. There are a few that are even cheaper. I wouldn't trust a $2,000 Pashley to one, but I don't mind it on this salvage job I'm working on.