In my experience and opinion, ear training is not only a waste of money, time and effort, it is completely junk in the way it is done. Ask me how I know.
It could be done differently and more effectively, but instead of arguing about that I'd ask the question: WHY?
Why in the world would you like to do ear training? Well, you may have several reasons and I won't argue with you about your motivations, but only about mine: I wanted to be more fluent in my musicianship. That's where ear training is junk. I think I can best explain myself as a spoken language example.
English is my second language and I struggled for years about it. I was terrified to say "paper" because I thought I could inadvertently wanting to say "sheet of paper" and instead say "shit of paper" and appear rude or worst to my hosts and coworkers. I tried "ear training" to identify correctly
eat - it
shit - sheet
bad - bed
but - boot
Results? Zero.
Only when I put myself into a child's attitude (with my own children and their friend) and started having fun with language in their company with echolalic's and other plays (ba-ba-ba-ma-ma-ma), I miraculously learned to hear, speak understand and be understood without any problem. Very fast. Except, it was not miraculous at all, that's just human beings learn language.
@Johnstaf hinted to this in a more subdued way, but let me double down: learning to recognize the intervals as traditionally done in ear training is a useless exercise. You might even learn to do it, but it won't make you any more musically fluent than learning to do instant 10-digit multiplications in your head would give you the Field Medal in Math. For example, a fourth and a fifth sound really close to each other. And rightly so, because they are the same thing! Depending what is up and what is down!
Instead, what you need is understanding the relationships in the context of harmony (full chords). And the good news is that you don't need any training for that: it appears to be innate or close to it. Play a major chord, then lower the third and make it minor. Do you need a training to recognize the difference? You don't, you just need to listen to music you like and try to play and have fun -- like a child having fun with words.
I have a lot more to say, but I don't have the time to say it all. I will definitely say a bit more in the context of your other question, @Austin
PS: sorry for being so blunt, I've wasted so much time, money and efforts with these things myself that I am mad with this traditional way of teaching
