These boards appear to have engine braking, but they also note that it's subject to fail on a steep hill or when the battery runs out: http://boostedboards.com/faq/
So— it'd probably be useful for a flattish, quietish commute of up to a few miles where storing a bicycle would be difficult. The learning curve also probably depends on your skills with reading traffic, e.g. if you've biked or motorcycled lately. (Driving helps too but won't necessarily give you an appropriate fear of big busy streets)
Riding is super fun :)
How are sidewalks with curbs?
Watch out for manhole covers.
I bought a nice ~$200 made in brooklyn longboard and started to use it.
It did cut down the commute time, and I liked riding it, but then I hit a pebble or something and was thrown forward, the board sliding across a busy street.
I am laying there, with a yellow cab having to swerve to not hit me, people honking, its amazing I didn't break anything, and me or my board didn't get run over.
Longboard wheels are just too small, too easily stopped. I gave up on it and just walked, not worth broken bones or a broken skull, and having to carry a helmet negates some of the benefit anyhow.
I would ride one if it had larger pneumatic tires and a foldable handlebar that would let you take a bump and stay on the board.
A lot of the challenge is in learning the roads and behavior of the drivers. I biked for ~ 3 years prior to getting my boosted board which contributed a lot towards knowing some of the "safer" routes.
That being said, your legs and calves will hurt like hell until you start to adjust to riding every single day. I go the gym 5x a week and still get achy calves from riding long distances.
I've only taken a single spill thanks to losing and regaining bluetooth connectivity going full throttle through a turn (mostly my own fault).
I can't recommend Boosted Boards enough. Extremely reliable piece of tech.