I've used Hermes quite a bit to send things during Covid where you don't have to go near others. Book and pay online, print the label, and take to a locker. Very convenient here.
Needed to send a jiffy bag which fell within the large letter size, but no stamps to hand.
So tried the RM online service - as I have a handy postbox.
Like Hermes, the file you print the label from is a PDF.
With the RM one, the label (about 1/2 A4 width) positioned to one side of the A4 sheet - the other side blank. With the barcode thingy also at that edge. Making it tricky to fix the label with sellotape without overlapping the barcode. Which Hermes says not to do - as it makes it impossible/difficult to read by machine.
Make you wonder if humans ever test these things in practice.