A 65km out and back last weekend along my favourite cycle trail led me to reappreciate the Trunk Bag, plus brought the opportunity to grab another pic of the bike with bag.
I've also recognised belatedly that a similar sized saddle bag would benefit from a decaleur, which would increase the weight of, say, a Carradice Pendle to match this Ortlieb product.
It also occurs to me that the 800g Trunk Bag must weigh little more than, say, an Ortlieb Ultimate Six handlebar bag and mount, while offering 40 per cent more capacity and better streamlining. Plus it has no effect on steering.
And if you carry the easily attached and very light shoulder strap, you can bring the Trunk Bag very comfortably into cafes et cetera. It removes as easily as a handlebar bag also, and more easily than a saddle bag.
Add all that up, and for day trips it is arguably rather superior to either, assuming you'll have a suitable rear rack attached in any case.
It is well named as a Trunk Bag, as it gives the bike a storage space analogous to the trunk - or boot, as we call it over here - of an automotive sedan. Usually it's not full, but nor does it get much in the way and there's a fair bit of space if you need it.
Its principle shortcoming arises from its very ability to avoid intruding. You forget it is there, which implies you wouldn't notice if suddenly it wasn't there. The risk of loss en-route is low, given that as I have said the mounting seems extremely secure. It's just that the consequence of such a loss would be high, if you treated it like a handlebar bag and put your phone and wallet in there. Resist that temptation and this is a very good product.