Having used a similar machine (150psi) for nearly 2 years, and now having upgraded to a much more powerful one, I'd say:
Yes you can clean carpets to a good standard using the 150psi machine - and there are advantages: smaller, lighter... easier to get up stairs, and into flats etc.
But, the higher power machines have their advantages too, as I've found out: For me the main ones are: faster cleaning, far greater reach (leave machine at front door), and better pickup (drier carpets).
Pay your money and take your choice.