As much as i would like to continue this conversation about Billy's tool.... i wont!
I don't exclusively use one line of products, i have to say SPM is a good product and it works very well, every job is different from the last one and a product could do a stunning job on one carpet and disappoint you on another.
Lets take MPower as an example... spilt milk in the foot well of a car... worked really well at killing the odour, the next day i used it on a sofa and it didnt do anything...
I think its important to carry a variety of cleaning solutions as every situation is different...