The drawback with regards to the Vonage app is that the Hangout extension is forwarding the call to the computer, not additionally routing calls to the computer...so if my computer is available, it takes cuts the line ahead of the Vonage app, and the Vonage app never rings.
A resulting issue with this is that the Hangouts extension only keeps track of Hangout conversations that originated from the app/extension, not phone calls (or text messages) that were routed to the Hangout App/Extension. What this means is if someone calls tries to set up a Hangout Call via the Hangout App and I miss it, I get a notification, but if someone attempts a regular phone call that rings on my computer and I miss it, the app/extension does not notify me or keep a history log of the attempted call. Additionally, since the call was never routed to my phone, there will be no record of a missed call there either. To get around this, I sign out of the Hangout extension on my computer if I don't plan on using it.