Well shit, I gotta go into autism mode again.
That's not very dangerous at all, lava doesn't dash.
It won't speed up until it reaches a steeper slope. If eruption at vent becomes more intense it can start going a little faster eventually but it won't be a sudden charge.
There really is no way a broad flow like this could "cascade" or "suddenly shift", it doesn't move like a turbulent avalanche.
These 'a'ā flows behave a bit like a caterpillar track, they're pretty predictable. All the solid chunks that are being carried to the front sit on top of the flow, you can see them coming and you'd know if any dangerous ones were about to fall.
This is all relatively low viscosity lava so it loses gas easily, away from vents there are no "pockets of pressure". It's viscous magma that traps gas and causes volcanoes to build up pressure and then blow up. On the other hand thin magma makes for mostly calm lava flows, this is the basic difference between explosive and effusive eruptions.
Hawaiian volcanoes rarely erupt explosively. Volcanic bombs could pose a threat in the immediate vicinity of vents but this type of volcanism produces few of those bombs. Most vents would also be surrounded by a lot of lava anyway so it would be hard for anyone to get close enough to get hit by debris.
Maybe the most dangerous thing would be a sudden explosion of steam if it gets trapped underground when groundwater comes in contact with magma. Once it's on the surface though even contact with water isn't catastrophic. For example formation of fresh pillow lavas is gentle enough that divers can get right up to the advancing front to take samples with basic hand tools.
Sudden wind change might be dangerous, it could carry toxic stuff like carbon monoxide. However in calm weather air will always rise above hot flows drawing a cool breeze towards lava.
This upward draft should take the hot and nasty stuff with it and give you enough time to move away in case of minor wind change. A storm could immediately blow it all in your face but, well, when a storm is coming you see it coming. Additionally Hawaii is known for persistent trade winds.
Guys in these videos aren't doing anything particularly dangerous or stupid. Unless you believe they will be punished by angry Pele or Hephaestus the outraged comments are unwarranted.