@Helen M it's a Brother4234. Not a year old yet. When I rang the dealer about a new blade I expected him to sell me blade replacement & a service (that's what I'd have done) as it's still under warranty. I'd have accepted & paid. Changing the blades was very simple, there's only one position they will fit. The new Chinese blade is the wrong shape to fit the machined recess. The upper blade seemed ok in the cutting position and sort of worked but when folded out of the way it hit the bottom of the lower blade. I turned it over by hand so found this out without causing damage. Unfortunately, on the advice of DH I ordered 2 more sets from the same company - and I've contacted to ask to cancel but it's too late
I expect DH will machine the blades down to match the original.
@Acorn @Ohsewsimple A useful lesson & I will try to get a refund from the supplier but don't hold out much hope. Will now order a genuine pair to keep in reserve.