I think I can chime in here as I had gone through exact same dilemma about 1 year ago...

I decided I settled with Topas Titanium carry-on trolley. However I was unsure whether to go with IATA or the larger model. The larger one is more than 50% bigger, which could be very useful.

Anyway, I did extensive research and made many phone calls in regards to this. What I was told, is that the non-IATA one will always be good when travelling domestically, and at times when travelling across the pond, and will likely get you to your destination. You may, and likely will, run into issues when your travel originates from Europe, as they are far more stingy there.

I settled with the IATA model, and it has been big enough. Of note, the IATA one is also just small enough to fit overhead when flying those smaller Embraer or Bombardier regional jets. Trust me, whenever checked at the gate, yours will rarely come back the same.