We chose these tea kettles on three factors: Ease of use, features and price.
Some of these tea makers are simple to use. Pour hot or cold water onto the desired flavour of tea leaves, and wait until the mix has reached its desired strength.
Others have extra features such as programmable strength, and will lift the basket out of the liquid when it reaches its desired strength or the machine will keep the liquid hot after it has brewed. The Ninja will brew both hot and cold tea, others are single use machines. The Breville and the Buydeem kettles will lift the infuser basket and keep the tea hot after it has brewed.
If price is an issue then the Brentwood and the Buydeem are the lowest cost options. The other models are significantly more expensive.