If one legged pedaling intervals are so popular, or should I say not particularly uncommon, then why don’t we see more emphasis towards hopping in run training?
Coaches invented them as something for bored athletes to do on the trainer during the winter.
Seriously though, they are actually pretty useful for diagnosing bike fit issues. If you can’t sit squre in your seat and pedal with one leg, your seat is probably TOO HIGH!!!
Interesting thought, might look into that. Can’t really say I’ve done them much. Are you supposed to be able to keep constant pressure on the chain? I find that when I have done them I get a huge whack we reengaging, after going over the top I think. Does that just mean I need more practice?
Yes, if you have a huge whack then you need to smooth out your pedal stroke. You shouldn’t have a dead spot like that when pedaling.
Try it with a counterweight on the opposing crank arm before you dismiss you pedal stroke as being “un-smooth”.
One legged pedalling “jerkiness” is not the same when two legs are involved. Given I don’t pedal one-legged it seems a pointless exercise.
Your feet are not connected to each other when you run. They are mechanically connected to each other when you pedal a bike. You’ll know if one leg is not doing its fair share of work when running (e.g. you’ll limp). When cycling, right/left technique imbalances can be masked since one leg can “cover” for the other during parts of the pedal stroke.
That makes sense to me.
You do. They are called run drills. Several come to mind the emphasis jumping.
And it could also be debated if coaches developed these to entertain athletes.
Should have put that line in pink. 
Seriously though, they can be a useful tool to identify bike fit and/or muscle imbalance issues.
In answer to the original posters Q, there will always be a little bit of a dead spot at the top of the stroke when pedaling with one leg which may be why you feel the chain tension slap as you get your foot over the top. If you drop your heel a little as you bring your foot around, you will notice that slap go away. Most people go really toes down when bringing the foot up and over when doing this drill. But, to be honest, I would worry more about being smooth through the bottom and backside of the stroke than over the top. They are a good drill to stave off boredom on the trainer and help smooth out pedal stroke which can help with efficiency on the bike.
If you are rocking on your saddle or really reaching through the bottom of your pedal stroke to get the pedal around, that is usually symptomatic of seat too high.