Sounds far better for a non public building where it's easier to ensure staff & visitor phones are registered - putting the onus on the member of the public to register their phone goes against the grain of the RRO and could end in tears....
There is no ensuring, there is no onus as this is a suppliment to the additional precautions.
Its talking about speeding up the process, rather than being found by a fire warden or waiting to see a beacon, the deaf person could already be notified and told where the fire assembly point is!!
The system we have now is not perfect, people rely on pager systems a lot which are often left on the desk while they use the facilities or left at home or out of battery plus cost £200 a time to get a new one!
This is a service that can offer an unlimited amount of users and uses existing technology.
Speak to the deaf community, what they have in place is not suitable and sufficient, they feel the risks are not as low as reasonably practicable, they like this system.
Texts costs normal rate and the system is £1k to add extra cover to an unlimited amount of users. Think about your local shopping centre's footfall each day. If 1 in 7 of those are deaf and they have extra precautions for £1k thats a bargain in my book.
Corporate Social Responsibility is a big thing.
You have also not thought about unmanned sites, this can notify FMs, engineers to the moment the fire alarm goes off thus speeding up the business emergency plan.