I've got a solution after several hours of trial-and-error.
Most apps and games are lean ipa/apk - they are downloading assets from the server during boot or shortly after a tutorial rather than bundling.
I was able to use a networking tool which captured all the incoming network requests.
I used the command-line-interface Wireshark, combined with Charles Proxy. This allowed me to record all the requests. The requests themselves were downloading to the assetcache folder which would encrypt them, although by directly going to the request URL myself I could point the download to a non-encrypted folder, ie Desktop.
Another tool I came across was Fiddler Everywhere. This would be my recommendation if you prefer graphic-user-interfaces.
With the files directly downloaded, they had the correct file-type, which in this game was .bundle as they were Unity engine assets.
I was able to explore these assets by expanding them with UABEANext.
Hopefully another ripper finds this useful.