I don't think your friend's quite right about that, if you're really watching every day! The ads are super annoying, no joke - after a while they really wear you down. Premium is definitely worth it for your situation with the train because you can actually download videos offline and watch them without internet. That's not just practical, it's great when your train connection is terrible again.
Just keep in mind: the offline downloads expire after 30 days, you gotta remember that. And honestly, it's also just nice to scroll without ads - you get rid of that annoying interruption, you just start the video and it plays. If you're on the train for long stretches anyway and watching every day, you're basically paying for a pretty chill month. The price isn't ridiculous, but with daily use it pays for itself pretty quick!