You asked, I am not going to give an opinion, but I am going to give you some facts you need to consider.
1) you are going to be signing a Non-Disclosure Agreement. This means if you leak something...even on accident, and then determine that it was detrimental to their development and/or cost them money, they can come after you for it. Are they going to? Probably not, but it's possible. That means you need to be VERY careful in what you say in public. That brings me to my second point
2) It puts a limited gag in your mouth for criticizing SC and CIG. If you like being an Avacado, you need to be sure that any criticism is based on facts, not opinions. Spreading FUD is looked at a lot harder if you are ETF.
3) you get the absolute WORST builds ever. If you thought 3.18 and 3.19 had a bad build and were horrible to play and would never play/test something like that if had any other choice...then you should say thank you but no thank you. ETF builds are horrible. If it takes 30 minutes for the server to crash, that's a great build. Many times the servers crash within minutes. So it's a race to find out what exactly is crashing things when everyone else is logging on. Is it something you are doing, someone else is doing, etc? I've seen builds that you log in, you try to get out of bed, and or press the door exit button, and the server crashes.
4) If you enjoy torturing yourself waiting for a bad build, hunting for bugs, and actually testing the mechanics, then yes, it can be a lot of fun.
5) if all you want is easy access so you can "play the game earlier" then subscribe or become concierge, because what you really want is Wave 1 access.
6) If you join ETF, there are a LOT of restrictions, including what you can do in-game. For instance, shooting other players is cause for them bouncing you from ETF. The only times you are allowed to shoot/kill other people is if you are both agreeing to it. It's not a "they logged in, so they agreed to it", it's a "Hey, I am testing out a mechanic that might be causing a crash. Could you let me shoot your ship and blow you up right after I turn off the communications satellite?" Answer "Yep, I can help with that. Is there a specific ship blowing up that seems to cause the problem? Does it happen on soft or hard kills or both?" They are there trying to help you get the data needed to find a crash bug. HOWEVER...I might be going to a normally PvP area to try and find a crash bug. If they just blow me up 30 steps into a 35 step process that took 20 minutes to setup without, I am going to be pissed, and more importantly, CIG isn't going to get the data they need to fix the bug.
7) It can be a lot of fun, and the people are great, but when you are there, you are there to test the game. Not play, not hang out, not be a badass, just to test the game and work with ETF people to find the problems so they can get it to Wave 1.