I had a Ohme smart charger fitted a few months ago and the process is pretty simple, ohme will contact you to arrange installation with one of they’re installation partners and they will ask you to fill in online survey form but you can ask for a onsite survey which is the way I would go.
My situation was very much like yours with armoured cable coming from my house consumer unit to my garage with a another small consumer unit that I hoped would be adequate, unfortunately it wasn’t, basically it wouldn’t have given enough power to the charger and the possibility of tripping out all the time. The way it was sorted was in the end far better and neater with a dedicated fuse and cable, slightly more in cost of £250 for the extra cable that was used, over 30m in the end.
So my advice is ask for a onsite survey.