The incredibly loud mechanical timer drove us all nuts. We always forgot to change the heating element (#slices) selector, so invariably ended up with one uncooked piece of bread. The pop up function is beefy but difficult to get escape velocity on small items. They eventually ditched it and went back to a £20 long slice Cookworks from Argos. They still have the Aga (also bloody annoying).
I paid about 3x what I would normally pay for a toaster for one on eBay. I expect it to last much more than 3x as long (a decent standard toaster usually lasts us around 3 years before something breaks unrepairably).
I personally like avoiding buying from manufacturers in places without modern labor laws and I frequently buy American made products, but for me anywhere in Europe is equivalent to America.
I would guess that the group of people for whom made in England is not sufficient and who would also spend $400 on a toaster is probably pretty tiny.
Dualit is in the UK and has been manufacturing high quality, hand built toaster for a long time, but most consumers would balk at the prices they ask for their appliances and I doubt you as a startup would be able to manufacture a toaster any cheaper.
https://www.dualit.com/collections/classic-toasters https://www.dualit.com/collections/spares
Frankly, I don't even own one, in spite of being a champion of the "buy it once" mentality. But it's on the bucket list.