Adam, you cant compare chems like for like. There's a reason you pay more for certain brands of chems. They work better, faster, protect your machinery etc
Speak to Matt at CleanSmart and go for something like a Airflex Storm, Turbo or the Pro. Basically, get a full sized machine now! I personally couldn't be bothered fannying about with a small extractor. Your going to constantly be emptying and filling... boring and tiring! Much bigger tanks makes a huge difference. And more power makes........?
Think of it as an investment in your business not an expense. An asset that you can sell if you need to.
I take my Storm up and down 3rd story tenements all day long. Weight is not an issue as long as the machine is empty.
The other benefit of having a more powerful machine is that you'll be able to do 50" to 100" hose runs. So you'll be able to leave your machine outside while you do the whole house. Or leave the machine in the hall way downstairs while doing the rooms upstairs.
If your still determined to get the smaller machine then I personally wouldn't go for the cub! I've heard nothing but bad reviews with the whole design and function of the machines (expect the odd exception). Do you really want all that stress with emptying the machine after every carpet? Sounds like a royal pain in the bum! For a lousy £200 go for the better machine. You can make that back with one job and more. You'll thank me later.
Oh, and if you do go for the cub report back to us after a few weeks and let us know how it worked out for you