I was recently down in the US (Los Angeles) and wanted to share my feedback and experience.
Prior to traveling I snagged the (on special at the time) "double" US boosters - data, voice calls and text - so three boosters in total. This gave me 1GB US data, 500 texts and 50 mins of US calling all for only $30! All three boosters clearly showed up (as US) in the phone services in the prepaid online account.
Upon touchdown in LAX I went off airplane mode and restarted my phone - Moto G5S plus unlocked (and yes it gets updates directly from Moto/Lenovo) using clean Android 7.1.1. After rebooting I enabled data roaming and then proceeded to manually search for networks. AT&T, TMobile and a few others showed up. I selected AT&T and after a few moments of registering I was roaming and received a text message from Koodo welcoming me to the US and reminding me that US boosters were needed etc.
At this point I was sending and receiving text messages back home. I was happily surprised to see mobile data working without any intervention as well, and picture MMS texts (send and receive) were good too. Texts messages correctly deducted from the online balances.
In terms of voice calls, I dialed my Koodo phone from my work Voip phone on my laptop (number based in Toronto) and it found the G5S without a hitch and caller ID was received as well. I left a voicemail and the VM indicator showed up on my handset. I checked for voice messages as normal and deleted the test voicemail. 1 minute of US calling was correctly deducted.
Based on my experience above and the low cost, US boosters are a super deal and amazing value especially since I still have lots of US voice, data and texts for my next visit - no more $7/day etc stuff!
Kudos to Koodo!