ok, have done a little more testing with this, against a captive portal enabled system on an Aruba AP-93.
The dir-505 seems to have some stability issues on the latest firmware, but technically does work as designed.
for public TOS hotspots, such as coffee chains or hotels that offer free w-fi via a captive portal page that uses TOS (Terms of service) ideally you want to use the Wi-Fi Hotspot option, simply to give you some level of protection on your own devices that you are connecting. It will actually pass through to the portal page and allow you to agree to the terms of service. It seemed to take a few restarts to "take" correctly however.