ITA was a good idea, in principle, because it was based on using one symbol for each of the 44ish sounds we use in spoken English words. something that our 26 symbol English alphabet can't do.
But of course, it wasn't practical because of the fact that to implement it properly would mean that the entire canon of English texts would have had to have been rewritten using ITA, and those not taught to use it would have had to have relearned a whole new alphabet. An utterly impossible task.
It did have some good spin offs in that it made some teachers look differently at the then 'conventional' Look and Say method of teaching reading, whereby children were expected to memorise words as 'wholes'. this is actually an impossibility as the human brain is only capable of memorising some 2 - 3,000 words like that and the English language contains at least half a million words...
Sue Lloyd, co-author of Jolly Phonics, taught it and she says that it helped her to understand how English words were constructed and to develop her phonics programme based on that knowledge. Phonics being the teaching of the symbols used to 'spell' each of the sounds in a word.
I learned to read in the '50s, way before ITA was tried out. I can't remember at all how I was taught, I was just one of the lucky ones who picked it up easily. But at least 25% of children struggle without being taught explicit structured phonics.