The problem with EV fires (as rare as they are) is that they are extremely hard to put out. Better to just let them burn out, or try to smother it with a specialty EV fire blanket. A fire extinguisher would be next to useless for this.
Now maybe you are doing it just for show (in which case it probably doesn't matter what kind of extinguisher you get!), but I would tend to agree with you: it will only confirm their unfounded fears of EV fires.
If you really want to make a statement, you could get the fire extinguisher and give it to THEM with the data showing that ICE fires are 10 times more likely than EV fires, so if they are worried about fires burning down the building, it would be best to have the fire extinguisher handy for their vehicles.