This is the best size for envelope addressing in my view and sits at about the centre of the available sizes. Small enough even for a DL or smaller envelope and yet allows a very legible label for up to 4 or 5 lines of text. A larger size (approximately triple the area) is best for A4 and larger envelopes or packages.
I use them for other purposes, too, especially for labelling folders and sometimes to add a permanent note to an existing document - it is neater than a scribble.
Easily loaded and removed should you need to use another size, they are delivered on a roll within a simple 'cassette' that drops into place. Once loaded, the labels self-align and are cut at the correct location when ejected.
Not unduly expensive for the numbers you get on a roll and easily available.
Very useful product and likely to lift in normal use.