Difference between I/Q mixer and I/Q demodulator

Hello.

I need a I/Q mixer (down converter). Transmitter signal is CW unmodulated. LO and RF frequency are same (4 GHz). HMC8193 is good, but its expensive. What is difference between I/Q mixer and I/Q demodulator? Can i use ADL5380 (I/Q demodulator) as a I/Q mixer? Why ADL5380 is very cheaper than HMC8193?

Do i need external LPF for filtering DC components, if i use HMC8193 or ADL5380?

Thank you.