DigitalOcean is quite expensive compared to GCE AWS and Vultur, but to answer your question yes it is. I ran a website with 2M monthly active users on their 5$ VPS
Not sure about that, as others have mentioned. At 2M monthly active users, bandwidth alone would be way more than $5 on GCE/AWS, no? How much bandwidth did you use?
https://uncrunched.com/2013/08/07/digital-ocean-v-aws-10x-pe... for an old comparison.
EC2 is, and always have been slow and expensive. its the other bits that make it compelling.