I did the CRI course and then did the FI course a couple of years later, so now I am a PPL with FI and CRI and without CPL TK.
The FI course was much more rigorous (30 hrs v 3 hrs, so that's pretty obvious). However, at the end of the course each had a test of about an hour. One 1 hour flying test is much like another; either way you are asked to teach a lesson to the 'student' (examiner) to an acceptable standard.
Whatever the content or difficulty or otherwise of the flying test, I sure as hell learned an awful lot more on the FI course.
My understanding (Whopity?) is that an FI without CPL TK can teach for the LAPL (clearly), cannot teach any element of the PPL (also clearly, even though the LAPL and PPL exercises are 95% identical), but can then teach the holder of a PPL to do other things (tailwheel and other differences, SEP rating, blah) including aerobatics if they are an aerobatics instructor.
The confusion comes from what CAA FCL (for UK licence holders) writes on the licence. Against the FI rating it says '... for LAPL(A) only'. But this is not the case as I can do the post PPL stuff on the FI rating!
To lake sure that I have as many bases as possible covered I actually insisted that CAA FCL leave the CRI qualification on my licence along with the FI rating so that there could be no question that I could do the post-PPL stuff - using the CRI if someone baulked at the FI qualification wording.