Do I need a pro-grade carpet cleaner?
Personally, given those two options, the size of the area, and the children, I would go with the pro-grade (Bissell).

Why?


Area: You plan to carpet clean a large area. The commercial/pro-grade carpet cleaners have an advantage here in their tank capacity which means fewer trips to fill and dump water.
Warranty: Heavy duty items tend to have longer warranties because they are generally built to withstand more use. The Bissell's warranty is 5 years versus the 2 year Hoover.
Satisfaction: The Bissell's overall review is a good deal better than the Hoover's.


Factors that might make you want the non-pro-grade cleaner instead:


Weight: Pro-grade clears will be heavier than the regular cleaners. They normally have large wheels at the back so you can take them up steps, but that is not as convenient  as a light weight model. So, if you have any sort of limitation in regards to lifting, the pro model may not be right for you.
Cost: Pro-grade models are always more expensive up-front. In the long run, you hope it's cheaper, but warranties and product life are a bit of a gamble.