Hey Sebastien,
thanks very much for your reply, and apologies for the delay in mine, I didn't get a notification on my email.
I have read up a bit on this matter on another thread Shelly Device Handlers for Hubitat - #232 by jihadd76
I'm guessing at this stage, it is already safe to use the HE built-in drivers with Shelly1.
I'm not familiar with Hubitat Package Manager, but I will look into it. I've mainly stuck with RuleMachine and Groups and Scenes, I haven't needed anything to complicated yet on my network.
Most importantly, is being able to have Shelly1 and the External Reed Sensor registered in HE, so that it can poll the device every x mins so it can check "if Open >3m then Close".
I'll give it a go by adding it directly to HE and then look into the HPM for further configuration. If I have any trouble, I'll be sure to update this thread.
Thank you for your help 