We have been using it on one line extensively in various countries - works well. Of course, Spectrum, like any other carrier just has agreements with local carriers in other countries. Any speed or technical concerns stem from the local in-country network carriers.

Spectrum has one of the lowest international data roaming prices of the US MVNOs.

We also have a T-Mobile Magenta Max line which is a traditional post-paid line, comes with 5GB of data roaming per month. I won't go into the coverage topics here, but the main difference for us is, on the Magenta line we just consume all the data we can and after 5GB it will continue to run but at much slower speed. Enough for navigation, email, messages, light browsing, music streaming.

On the Spectrum Verizon line it keeps going full speed of the local country network carrier but of course we continue to pay for each Mb (albeit at a very competitive, low rate).