Hangout notifications in Enhanced SMS & Caller ID + can be enabled either through "Other Apps" or via the Compatibility setting under Gtalk options. There are pros and cons to both methods and it is up to you to decide which one suites you best. The compatibility option does enable our internal Gtalk client and this does require an active data connection running through a background service. This could be hard on your battery depending on the number of Gmail accounts you enable on your device. Using the "Other Apps" method is quite efficient but can result in only the first message being read out and subsequent messages read out as "Eddie - 2 new messages", etc.
Assuming that you have decided to use our internal client, we have found that the best way to receive consistent messages is to enable Hangouts in Gmail. To enable Hangouts in Gmail, click on your profile photo from the Google Talk chat list, then select Try the new Hangouts. Hangouts will immediately replace Talk, then walk you through a very brief introduction to Hangouts.
Do let us know if this was useful to you and thank you for supporting Enhanced SMS & Caller ID!