As far as I’m aware, any software that can result in a game that is playable is accepted here. I’m not familiar with Squiffy, but if it exports game that are playable with just HTML, then I don’t see why they can’t be here.
In Game Dev, a lot of times it doesn’t matter what tool you use. A lot of techniques are usually specific to programming in general, regardless of the language/tool used. The best way to learn more, is to keep making games with the tool you have the most experience in. If you ever feel like trying a different tool, go for it, but be prepared to spend some time learning it.
At some point it will not matter what tools you use, and you can easily adapt to any tool in front of you.