I can answer some of the questions for you from my experience and own opinion
My dd & friends have said it required techniques only taught in further maths
This is totally not true. There is a question on series which could be solved quicker with FM knowledge but it is not necessary at all. FM students generally have better mathematical knowledge and know more advanced techniques so they can solve a problem in more than one way.
that some of the material was either not on the spec
Everything is in the spec. It is down to the students, teachers and schools to teach it.
was asked in such a different form from the sample questions & textbooks that it made it difficult to know how to approach the questions.
This is true but only partly true. In the legacy spec, all Edexcel papers are pretty much the same year on year. Students just need to do a few past papers and they pretty much would see the same thing in the real paper. Teachers were used to the format of the exam and could skip many things because the chance of they ever turned up was almost zero.
Fast forward to present day, with any new spec, teachers have no idea what will be in the paper so they will either teach in the same way as before, hoping the paper will be set in the same manner as before or try to teach everything but not in enough depth. It is not the first time Edexcel changed their spec with a lot of warning about increased difficulty but in the end the change was minimal. Some teachers I used to teach with still using the same textbook. This will take a couple of years for people to adjust, develop resources and knowing how to teach it better.
My view of the new spec is it is consistent with what Edexcel has been doing with the GCSE spec. It is harder, which means students really need to change two things. Learn their Maths properly, not by rote but gaining a full understanding of everything that they study. Secondly, they need to change their expectation of how to do a Maths paper. Don’t expect to complete the paper but go over the paper, concentrate on a few questions, spend more time on each of them but do them very well.
Schools need to change their approach as well. Letting grade 5 or 6 students taking A Level Maths will surely end in disaster. AS exam would need to go eventually except in special cases so the end of year 12 could be used for teaching.
I am not arguing that the change is good or bad. It is what it is and how to deal with its present form.