It’s possible for anyone to search the app store, it’s not ‘members only’;
Search engines also show you the way to the app store:
(this is meant as helpful information, not to point fingers and such 
)
You can view the supported devices by opening the app page:
https://homey.app/a/com.heltun/
You can send custom z-wave commands to a node with Homey:
IF the device supports setting positions per the Heltun app. When unsure, mail to Heltun support, support links are available at the app page at homey.app.
When it’s there’s no problem using positions, it should be possible by using a so called advanced virtual device.
A sidenote about HA, I also run HA next to Homey, and here it functions mainly as device support ‘interface’ atm. With help of the Home Assistant Community app those devices can be added to Homey, and use them as if it were native Homey devices.
While you mention having 300 (Three hundred…) devices, maybe it’s smart to let HA do some of the work as well. Homey’s z-wave and zigbee implementations are not top-notch to be honest, BUT it depends of course on the devices, interference and the PEBCAK 
