So you're spending ~$80 per year for DO plus $180 for the hardware. Over 5 years that's $580 (if that Chromebook really makes it to 5 years and DO's prices remain unchanged). This is about half of what you'd have to spend on a local dev setup with similar capabilities.
Not bad, but I think whether or not it makes sense depends entirely on the productivity difference between the two setups.
Not bad, but I think whether or not it makes sense depends entirely on the productivity difference between the two setups.