I purchased a second hand inline heater a while back and it has been very useful especially on the real mingers using powerburst.
When Ash told me that a CRB would change the way i would work i was very interested, up until this point i had been using SPM and a sebo duo and the results had been acceptable.
Its when you are brushing in your pre spray with a TM4 and the carpet starts to look loads better when you know something really cool is happening, pile is lifted and that almost new feeling under the feet can be felt.
Where a TM is so much more powerful i guess it doesn't rely so much on the agitation process, so a CRB machine would be the next thing i would add to your gear mate!