A review of JJ's House that made me smile said that it was "too good to be true, & too good to be good" ...!!!
Both experiences & quality seem mixed in reviews about it. Everything's made in China - which is of course not a bad thing in & of itself - half the clothes on the high street are.
But because you're dealing with them directly without a middleman, it's a) cheaper - a big plus to loads of people of course, but also b) returns/issues are just between you & them as you don't have the leverage or influence of being a company that's a major client - & that would be a big minus to me.
The recurring issues seem to be quality/things looking different/fabrics being poor, or delays, difficulty with returns, & - most of all - having to get things altered to fit properly, so any savings are lost.
It looks like most of the dresses from Needle & Thread are made in India. Their ethical statement is really impressive, & they get really good reviews overall.
So personally I'd prefer somewhere like that (if I wasn't going for vintage, which would be my own preference).
That said, when my sister was getting married 15 years ago, she came to visit me in Edinburgh & we did a trawl around the wedding shops & department stores. I was horrified at what was on offer from supposedly high-end labels!! Synthetics galore, itchy scratchy lace, shiny fabrics ... & having the word "bridal" tacked onto it seemed to be licence to charge several thousand pounds for something that had cost probably £50 in fabric & labour - in a factory in China ... maybe the same ones used by JJ's House ...!! The profit margins are obscene.
My sister ended up getting a pure silk chiffon & lace wedding dress for under £200 from Monsoon - & it was far lovelier & more expensive looking than others at 10 x the price!!