External data within Nintex Form

Hi everyone,

I'm looking to get a drop-down menu within a Nintex form populated from an external database.

After some investigation there are several options that I have come across:

1. JavaScript - this involves exposing a connection string to the client side and not acceptable for the current environment.
2. Nintex Action Pack - ProSymmetry​. I've requested a demo and will investigate the security and ease of use.
3. Timed workflows - Nintex workflow to query the required data and store within a SharePoint list.  This would never be 'live' data and if running multiple times per day there may be moment when the list is empty awaiting population of data.
4. External BCS list - unknown area for me. 
   1. If we used BCS to create an external list could this data be used within a Nintex form?
   2. Would this data be live?

Are there any other options which are worth investigating?  In addition can anyone expand on the ins and outs of using BCS?

Thanks.