The short answer
The work itself
On Siargao we worked from one place, CoCo Space, which runs Starlink, solar panels and a backup generator. That combination matters more than it sounds, because it kept us online when the rest of town lost power. On an island, a single good workspace is worth more than a choice of ten mediocre ones.
In Chiang Mai we mostly rotated between cafes and the apartment, which gave the day some variation. Proper coworking exists if you need a fixed desk or a community, and the city is large enough that you are never far from somewhere to sit.
The difference: Siargao gives you one dependable place. Chiang Mai gives you endless options. If you like routine, that favours Siargao. If you get restless in the same chair, Chiang Mai.
What it costs
For Siargao we tracked what a month actually cost the two of us, and the calculator in that Blueprint is built on our own numbers, including flights. See the breakdown.
For Chiang Mai we did not keep accounts, so the calculator there is an estimate built on public price data rather than on our own spending, and it says so on the page. It still tells you the useful thing: Chiang Mai comes out meaningfully cheaper, mostly on rent, and food in particular costs very little because street kitchens and markets are good enough that cooking at home rarely pays off. See the estimate.
The honest version: the Siargao numbers are ours and the Chiang Mai ones are researched. Both are labelled that way, so you know which is which.
Getting around
If riding a scooter in traffic worries you, that is a real argument for Chiang Mai. On Siargao you would be choosing to depend on it.
The hours you are not working
Siargao is surf, water and daylight. The reward is right outside, which is exactly why the guide argues for treating the ocean as something you earn at the end of a work block rather than something you drift into at eleven in the morning.
Chiang Mai is temples, food, night markets and mountains, plus Pai a few hours away for a weekend. The distractions are more varied and easier to postpone, which is either an advantage or a loss depending on why you came.
When to go, and what to avoid
Both places have months you should plan around, but only one of them is dangerous to get wrong.
Our take
If the writing or the work is the point, and you want the fewest possible obstacles, go to Chiang Mai. It is cheaper, easier, better connected, and you can have a bad day without it costing you anything.
If you want the month to change something, go to Siargao. It asks more of you, the logistics are less forgiving, and that is rather the point.
We would not tell anyone to do both in one trip. They are eight hours apart by air and they reward completely different rhythms.