Oanda is well known market maker
Was in VIP @ MFF for several months, so it was revealed in the CFTC case that group was A book
Interactive brokers had L2 market depth, Time of sales, partial fills & you could place limits within the spread instantly changing spread like a true ECN. You have WAY more broker knowledge than I do, but I've never seen a FX broker operate like that in the US that was B book.