Here is Alexa's first day report:
All my items (lunchbox, 500 page paperback, umbrella, keys, two phones and various other gubbins) fitted in nicely. Still have plenty of room for more stuff if needed.
When carried by the top handle, the bag did not sag too much but does tend to bend a little inwards. Worry that the leather where the bend happens may crease/age more quickly than rest of bag.
Bit of a faff when wanting to get into bag quickly, having to open postmans lock and unclip magnectic straps.
Carrying on shoulder strap is comfortable, and the top handle is great for grabbing when running for a train!
Here are pictures of a fully loaded Alexa in action.