"Why not make Horse as an extension for other browsers?"
Because it isn’t possible; extensions are not given the permissions required for Trails to work. So it has to be a separate browser.
"How is Horse different from extensions like Tree Style Tabs, etc?"
The same way a bicycle is different from a wheel; it is one part, but Horse combines it with a few other features to create a unique experience.
"Will you be adding extension support to Horse?"
Eventually, but doing so requires an enormous budget, which I don't have yet. For now, Horse has Adblock and Dark Reader built-in. With a Password Manager and Page Translation on the roadmap.
"Why does it cost money?"
Horse needs to make money to keep development going, because Horse is not backed by investors. This is a good thing; you are not the product, the browser is. I can focus on making a great tool for you.
Why Is there no free trial?”
I currently don’t have the bandwidth to add free trials, but try monthly and I’ll give you a full refund if it doesn’t fit your needs.