I run with a Chariot Cougar 1 in run mode. Some comments to consider (not sure how much it applies to others but things to look out for).
The Cougar is modular so the run mode is a single wheel that you clip into the front. Tracking is much more critical at running pace than walking and so something that is either very fixed or easy to fine tune is good.
The catch strap isn’t really long enough for me and is fixed on the left hand side where as I prefer to run holding with my right so I’ve had to rig another. I initially was skeptical of the strap but downhill you’re only one trip away from loosing control (see next point)
It’s amazing how fast 50lb of Chariot + toddler accelerates downhill. Some versions come with disk brakes and if I ran more I’d seriously consider a braked version.
It’s amazing how slow 50lb of Chariot + toddler can be when you’re pushing uphill.
I tried all sorts of add-ons for bottles and the like but they just added phaff.