One of the first things you should think about when getting a hot tub for your garden, is where is it going to go?
You will need to have quiet a big garden for one, and will have to think will you use it enough.
For an outdoor tub, you need somewhere that is level and solid so that the tub can sit nicely on it. You will also have to have power nearby to plug it in. Also, the logistics need be thought about. Hot tubs are big, and will you be able to get it to your back garden. Is your gate big enough? What if the only access to the back garden is through the house?
Something to solve all these issues is to look at an inflatable hot tub as these can be stored away easily, are cheaper and are a lot more realistic for people to own.