Plastic cable tray ? - that's a new one. Have you got any examples of this as I'd be curious to see it.
As for tie wraps it generally looks good, however, I gather that there is a requirement or part of a wish list from the fire brigade that metal tie wraps should be used where there is no earthed containment. I believe there is also additions to this wish list that plastic trunking is dangerous, particularly when heated up in a fire as it melts and drips smoking PVC all over their new outfits......