Can you please let me know what 'Units' are that you must select before placing a booking? There is no label, or description and I do not know why this is here. Please see attached screenshot and also let me know where to change this to something useful. Thanks

Hi,
"Units" is number of room in search form. In home page, you can see unit default set to 1 and if you click onto "CHANGE SEARCH", you go to full search form and there is a field named "ROOMS = UNITS". When you change value of Units, you can see number of room changed.
You can please customize number of units to display in admin/rooms/config/bookings > tab "ROOMS AVAILABITY SEARCH SETTINGS".