The issue is that this offering is complex to understand as opposed to DO which is incredibly simple to understand. It is actually pretty funny how hard it is to understand this offering from AWS, it takes many paragraphs of reading to figure it out.
There's nothing to understand with DO because they don't tell you what their definition of a "CPU" is. For all I know it could be oversubscribed in a worse way than EC2.
Most people don't care the exact speed of the CPU for a server, as long as it's stable and doesn't lockup with little load, especially when purchasing a Micro instance. If CPU utilization is high then it's time to upgrade to another CPU or start another instance if possible.
It would be better to do real speed tests of each service to determine average "CPU" speed. I'm sure both services are constantly optimizing for both shared hardware usage and speed, so the stats would have to be updated regularly.
AWS is a simple model: pay for what you use. Most cheap hosts (i.e. please kill me DreamHost) give you no SLA and your rolling the uptime dice. Three years on DH and I wanted to kill myself. Three years on AWS and life is just splendid!
To understand your billing, you need to understand what you're consuming, which you always should. These credits add a little wrinkle, but also make the service cheaper and more deterministic. If you have credits, you'll get the CPU you bought with them.
