It’s easier to pour if the handle is on the side of the teapot.
A round, squat shape is supposed to make a better brew by allowing the leaves to move around more. So, it defeats the object if you have an in-pot strainer. A good excuse to buy a good old-fashioned tea strainer.
Japanese cast iron teapots are made to sit on a wee heater, which is why they’re made of metal and have the handle on top. The handle is often detachable and so moves when you pour. That’s fun!
Signed, someone who has rediscovered the joys of real tea, has about 10 teapots, and none of them are ‘quite right’!