Claudio - the question if a power meter (PM from here) worth it or not, highly depends on your personal targets with your training. If you simply enjoy cycling and want to pass the time while you can’t ride outside, a wheel on smart trainer will do it.
If you want to get into more serious training with quick reactive trainers because the short interval work with big power differences means something to you, than invest in a direct drive trainer (DD).
If you want to have consistent results, accountability, and investing long hours into (in most cases) race preparation, than PM is the way. For example Vector 3 / Favero Assioma / Pwer2Max NGeco / Stages Dual / etc.
So it start from your needs. I know it’s not the answer to your original question, but it is a different aspect to consider before buying a PM.