I tried RealFlight and neXt with the latter being my favorite. I use Spektrum InterLink DX simulator controller to fly it.

Time Scale

Slowing down simulator's time was the best thing I have discovered. Start at 50% and gradually increase while working on a maneveur.

neXt

Modern advanced RC heli simulator. Multi-platform (Win, Mac, Linux). Advanced heli training modes: hover trainer, piro trainer, landing trainer.

neXt on Linux

The neXt on Linux has joystick calibration utility which doesn't compile anymore. By default joystick will have big dead zone. To solve it launch the sim with:

evdev-joystick \
    --evdev /dev/input/by-id/usb-Spektrum_InterLinkDX_2063354E4652-event-joystick \
    -d 0 && \
    ~/Packages/neXt/neXt.x86_64

Binding Time Scale

You can assign the simulation speed to a transmitter channel. Settings > Input Device > Functions and pree o. You will be able to bind time scale.