While gaiwans are really good for oolongs, I find them rather unusable for sencha: sencha particles are too fine and spill out of the gaiwan with the brew. For fine teas like sencha, gyokuro, etc. I use an infuser with button, it works the best for me.
Discussion
I have a tea strainer. Personally, I currently have more trouble with teas that are brewed at temperatures around 95-100°C (like hojicha, for example). This gaiwan heats up incredibly fast 😅. But I think it’s more a matter of skill.