iOS beta testing is an absolute nightmare!
You can manually add test users UDIDs to your provisioning profile in your Apple Developer portal. You then create an Ad Hoc provisioning profile and attach the test users UDIDs to it. In xCode you build and Archive for AdHoc which makes an IPA file that your beta testers can manually install through an iTunes app running on PC/Mac. It is a very convoluted process and confusing to beta testers. We had about 50% of our iOS beta testers have issues with the procedure and many of those gave up trying (who has time for all of that?). Plus Apple restricts you to 100 test devices - lifetime total for a dev (I think this is the main advantage of TestFlight - it can do more)!!
I still use it on a handful of beta testers that are experienced with the process.
I can personally test it on my 3GS, but that is the only device I have available to me. My testers will likely not be open to testing for other folks otherwise I'd ask some of them. It is so much of a hassle. I can also help guide you on getting it to work. Just shoot me an email.
It also depends on what you're looking for out of a beta test. Are you looking for compatibility? Are you looking for playtesting? If it is compatibility then you can run the game in the simulators and be pretty sure that is how it will work on live devices (other than the major lack in frame rate - but you can at least test functionality - can't do IAP or push that way though).
If you're looking for playtesting I'd highly highly suggest building an android APK and doing IndieDB as well as posting here for help. I'd definitely help you out. Also with Android you can simply upload a beta to the store, set up a google group with your test users, and send them a download link. The advantage of that is it will capture crash reports, allow IAP and push. If no features like that then it is simpler to just ask around and distribute the APK.