So who do I believe as both arguements seem valid
Both arguments are, at their core, valid.
Can I say that I am currently sat about 6 feet away from a man who has spent the last 15 years of his life ensuring the Electromagnetic Compatibility of airborne equipment. It is a massive job to ensure that equipment that is fitted to an aircraft doesn't interfere with each other, let alone introducing unknown quantities. All electrical/electronic devices emit RF and all are susceptible. All we are talking about are the differences in level and whether the equipment continues to funtion as designed at those levels. If this is all bull, then the aircraft manufacturers are spending a fortune trying to design out something that doesn't happen, not to mention having aircraft carry a large amount of weight in shielding and filters etc. The fact we don't see that many incidents is a tribute to those that practice the art of EMC design. They will be the first to admit that they can't mitigate for everything though. Hence the rule, it is a precaution. Just like fastening your seatbelt, if everything goes to plan then you won't need it. But if it goes wrong it has the potential to go very wrong, so why take the risk?
As for the argument that they want you paying attention during these phases, I absolutely agree with that too. I pay attention as if my life might depend on it, strangely enough it might. Yes, I am that man on the 'plane that gets irritated if you don't put your tray table up, return your seat to the upright position, and my pet hate, leave your laptop on the seat next to you. I get irritated because someone has decided to lower my chances in the incredibly unlikely event of something happening. I think that is just the height of discourtesy. But I also understand that the average person does not understand that an aircraft seat has been designed to provide protection but only under certain conditions. I also understand that the average person doesn't really appreciate the fact that a 5kg laptop, in a 10g crash will seem as if it was 50kg. So i politely ask them to comply with the rules, written by those who do understand.
If the pilot wants to break these rules, well they are in charge I trust them to fly me, I'll trust them to use their I-Pad safely whilst doing it.