Is the power accuracy gotten better. I hear many reports of this unit not reporting power correct mostly under reporting

I have the same isues with under reporting power. I didn't realize it until I had a PM for outdoor riding this summer.

It seems to be accurate around 200W, but under reporting up to 40W at 300W. So different accuracy in different power zones, which is quite dissapointing for a turbo trainer. This completly messes with what I'm acutally putting out on the trainer and therefore my power zones.

I now use the PM for power reading on the trainer in the big front ring (inertia of higher flywheel speed keeps the flucutation of the resistance lower with PM).

Thanks for reaching out! Without a second source of power data, all we can compare your new Flux 2 to is your perceived exertion and this is subjective.

No two power meters will measure exactly the same, despite their factory calibrations or claimed accuracy. It is expected that a smart trainer and a standalone power meter will report different values, but the two power measurements should be relatively accurate to one another.

The Flux 2 measures power where resistance is applied (at the rear hub), and this will typically be a lower measurement when compared to a crank or pedal-based power meter due to drivetrain losses.
Please review My Power Meter Output Is Different From My Smart Trainer for more details.

FTP tests are intended to push your limits in order to get an accurate assessment of your max potential. I would suggest performing a new FTP test, and expect it to be very difficult when done correctly.

If you experience a concern that your Flux 2 is under reporting power, please contact Garmin support for your region: https://support.garmin.com/