Do any of you use a fixie or track bike on Zwift? My intention is to have a permanent bike on the trainer and I can pick up a good deal on a fixie. The trainer I have is the Elite Qubo Fluid with power meter, this model has no resistance adjustment but the faster you pedal it creates more resistance and it has that road feel. Appreciate any helpful comment, thank you.
I was thinking the same thing Fernando, I reckon it would be ok on flat courses but I would hate to climb to the mast on Watopia on a fixed gear! 
My experience with a fixed-gear on the Computrainer was so-so … the correspondence is not true 1:1, so the resistive benefits one gets with fixed gear on the road are absent.
You’re thus left with a singlespeed, which in the trainer environment is probably of no benefit whatsoever (it’s not as if the weight savings in the drivetrain and simplicity of no shifting mean anything mounted on the trainer, as they do on the road).
Fixie? Don’t change the gear and you have exact what you’re looking for.