I worked in a college which had Evac Chairs so have some knowledge.
The user has to be able to self-transfer from their wheelchair into the Evac Chair, so they cannot be used by every wheelchair user.
The operator has to be trained in how to use them. It’s not intuitive.
They’re heavy with someone sitting in them. Not everyone will be able to operate them.
They’re definitely a useful contribution to emergency evacuations but they’re not the only answer. Our preferred strategy was to timetable wheelchair users in ground floor rooms.