On the iPhone the sim card easily ejects from the side and you don't have to turn off the phone to remove/insert.

I have about 4 of those SIM adapters - they came with my SIM cutting tool.

No, it's not "easier" to eject and swap a SIM in any case. But it is easier on the wallet if you have to pay an additional $20 a month for tethering or using your phone as a hotspot.

Anyway, it's moot if ATT has the profile set up to be iPhone (or phone) specific and doesn't allow swapping.

Currently I have two different SIM cards myself. One is voice only and the other is data only. I swap once in a while, but I don't normally carry both cards on me. Usually I have the data card and on the odd occasion I need to make a voice call I use voip. I was supposed to be using a dual SIM adapter by now, but the one I bought on eBay never showed up (got a refund).