Brian Gaff was thinking very hard :
I have been told that when they alert me to fit mine, I have to ring up and
be sure they fit the accessible one, the one with the voice. would you not
have thought that cost wise it would have been just as cheap to fit them all
with this function and you could turn it off. Seems a wasteful way of going
on. However apparently the units for single fuel and economy 7 are still not
ready apparently.

One thing to be aware of, is that the trigger points for higher
consumption levels are not user adjustable. Our IHD has tri-colour
LED's to show when an instantaneous consumption level is exceeded.
Every time the boiler fires up, the gas LED turns red, when not lit, it
shows green. Likewise the 'speedo' style LCD display just gets pinned
to the full scale when the boiler fires.

I suspect your voice version would only offer similar low/medium/high
consumption voice output. Much more useful to you, will be the values
shown on the suppliers web site.