I would prefer 2K res on a laptop. On a 15 inch screen, 4K is overkill - I have to increase desktop scaling to read text, so there's no increase in screen real estate. Higher res drains the battery faster as well.
Was it not a matter of leaving out a country code or something? I was getting 200 OKs and not receiving messages, until I realized that my number without a +1 in front is a valid Peruvian number.
I've had a similar experience. I've used their api to send SMS for multiple projects and have no complaints in terms of delivery.
Their web UI is pretty buggy. Certain parts of their control panel sometimes causes my browser tab to freeze. Recently I found that pressing tab caused the page reload when filling out verification info for buying a new number.