It isn't clear to me whether or not the old TestFlight service can still be used for testing iOS apps. I've seen a lot of information from various places about iTunes Connect, external users, internal users, limitations, etc, but nothing about the old service.
Do I have to go through iTunes Connect to test early versions of my app or can I use the old TestFlight service where I provisioned devices using the UDID? One of the reasons I ask is because of Apple's TestFlight app that was recently released that only supports iOS8 - our device target is iOS7 and below so it doesn't seem we can even utilize that service.
Yes, it is possible to still use the old TestFlight instead of Apple's TestFlight. However, to use the old TestFlight, you need to have already signed up for an account before they partially shut down.
Apple has officially shut down the old TestFlight.
If you don't have an account, yet still want the freedom of the old TestFlight, you might try testing out HockeyApp, however it does cost money.