I am not sure the last time you used Test Flight, but it has changed a lot in the last year. There can still be headaches with it, but since it was bought by Apple you now distribute your App through iTunes Connect which is the same way you would do it for releasing in the App store. You have a number of beta testers (up to 1000) that all you need is their email address. You can also have internal testers (up to 25 I think) which will get every build you upload automatically (however they do have some access to the information about your app through their iTunes accounts).
So in summary it takes the same amount of work and the same process to have beta testers that it does to release it through the App Store except that you don't have to wait the 5+ days for the App review. Do note that the beta version will expire after 30 days at which point you just need to upload a new one.