Millettia are tropical/sub tropical plants and are not related to Wisteria in any way. The one offered for sale as 'evergreen wisteria' is Millettia reticulata, reputed to be hardy in zone 8 or Zone 7, depending on how optimistic or desperate to sell the supplier is, but they're about as likely to be evergreen in the UK as pigs are to fly. Not sure how you'll grow it in the front of your garden, unless you've got a supporting wall for it there; if it survives, it gets up to 30 feet. Grows well in the Indies, parts of China and Africa

http://www.houzz.com/ideabooks/55161335/list/great-design-plant-millettia-reticulata

so the reason you never see it is that its only maybe hardy down in cornwall or somewhere like that

Yea, in sheltered warm spots, or Jersey or the Scilly Isles. Depressingly, if you find an unusual plant you've not seen anywhere before, its usually because it doesn't survive our winters, well, that's been my experience down the years... and that's a lot of years now!