To be fair, this is only used in an emergency if you run out of battery charge. It's akin to calling AAA and having a 5 gallon can of gas delivered to you on the side of the road.

I've owned two electric cars over the course of six years. Never had to use this service, although we have occasionally drove into the charger on a very low charge.

We have a slow charger at home, and usually leave the car plugged in to trickle charge overnight. That's good enough for driving around town. If you want to take a road trip or do some extended back-and-forth driving more than 100 miles, you need to use a quick charger. You will see these in grocery store parking lots and malls. It takes about 20 minutes to fill the car up to 80% charge and another 20 minutes to get to 100% charge. If you plan your trip accordingly, you can quick charge while you shop. Online maps are available with the locations of quick chargers and the distance between them, so you can plan your trips carefully.

The only problem with electric cars is that they are so popular, the quick chargers are often busy and you sometimes have to wait for other people to charge before you can do it. Also, occasionally some asshole in a gas car will park in the spot and prevent you from using it. (Just being obnoxious or being oblivious to the many signs pointing out that you are not supposed to do this. This would be solved by making it an instant tow-away zone and people would stop doing it.)

As the popularity of the electric cars has risen, they are outpacing the availability of public chargers. These were installed and maintained by a private company that got a government grant. The grant was just to install the system, not maintain it. Sometimes the chargers are broken, and the company is slow to fix them. Since they were paid by the government grant to install them, not to maintain them, they are not incentivized to be quick to repair them when they break. (The brand name of this public charger system is Blink.)

The system is beginning to show its growing pains and is sometimes a pain. But it largely works well. I love driving an electric car. They are fun to drive and really fast. If someone else would invest in a another quick charge system to compete with Blink, and actually maintain their equipment, it would solve both the congestion problem and also the problem of arriving at a charger and not knowing if it is going to work or not. It's not like you have a lot of choices at this point. That's really the only problem with the system, and why these emergency trucks exist at all.