USPS seems to me to be a waste of time?
Such a pity there wasn't a shipping option?
Even Fedex is a better bet.
[I have a US Ford old car....for which spares, etc are plentiful. [1967] and I get most of the necessaries from a US parts dealer [RockAuto].
As an example, this summer I ordered a full gasket & seal kit for its power steering. Around £100 plus delivery from UK specialist dealer....£70, delivered, including all taxes & duties paid, from Rock Auto, via Fedex. Not for just the one item, but 2 separate kits plus a hydraulic hose [as a spare]!!
Ordered on the Monday, at my front door Friday morning.
Despite the [sometimes only slightly] increased shipping costs, I would use Fedex or DHL in preference to any postal service...even Parcelforce!
If only for the one-off payment! [Never mind the speed of delivery]
I bought a couple of HO B/mann 4-4-0s [moderns, not old-time] from Trainworld some years ago now [they've sat in their boxes ever since]...and a Russian Decapod [similar].... I chose the DHL shipping option, despite the slightly increased cost over USPS...I recall ordering them on the Monday, and getting a knock on my front door by DHL on the Thursday. None of this 'demand for payment, and a fee for the pleasure of doing it' lark from the likes of PArcelforce!
Or the tracking that shows items taking ''barely 3 days to get from the USA to a UK airport, and two weeks of sitting in various UK warehouses'' malarkey.