Neil,
Can't understand what your argument is and why you are comparing it to the Prowler and not all TM's.
I agree the generator will allow you to run your portable at whatever it'ss performance limitations are, however you will still need to find a water source for it though.
As I understand it the benefit of the Prowler, or any other TM is not just that you no longer require a power source but that you are supposedly taking the limitations of your portable to a new level, ie, more power, more vacuum, with no need to stop to refill and empty.
I'm a porty user and have previously looked at generators of these output, however all the ones I have viewed of a reasonable quality have been £1000+.
This one from Aldi looks like a bargain, but how reliable is it?
As a comparison, I have a pressure washer that I bought new from ebay for a bargain price, it's a chinese honda copy import. It ran ok for a couple of months but now it's sat at the back of the garage with a u/s pump and nowhere to get parts for it. I now have a Honda GX390 13Hp pressure washer that runs all day without a hiccup.
You get what you pay for.