Will an iPhone8 bought from Virgin Mobile work with international carriers after it has been unlocked by the carrier?

Will an iphone8 locked to Virgin Mobile work fine with international GSM carriers after it has been unlocked? I have heard that carrier branded iPhones are meant to optimize service on a particular carrier.

I plan to buy an iPhone8 from VM but intend to use it during international travel later in the year. VM has confirmed that they will unlock the phone after 14 days of use after which it will be compatible with all CDMA/GSM carriers both in the US as well as abroad.

But I would like the Apple Community's perspective on potential pitfalls.

Thanks

p.s. I would have preferred to buy a SIM-free iphone from Apple and then port it over to VM but it is unclear if the promotional plan that I want to get with VM will work with a SIM-free phone bought from Apple. Which is why I am having to buy the iphone from VM and then getting it unlocked.