[mark dew]

"Making the customer happy" is really quite a good business advantage if you think about it. 

yes i understand that. A happy customer is the goal.
But what about the customers who are happy with the finish with wfp but who would prefer to see you there working away for 1/2 hour with a cloth in hand when 10 minutes wfp will make them just as happy about the finish.
I don't have a great experience but have yet to come across a job that is better using 2 different tools to do the outsides. Though i have had a few where i had to detail afterwards. But it has always been a temporary way to give a good finish.

[Captain Scarlet]

VENTS arggggggg. I have never had a problem with them with my customers, simply because I never touched them. Then I did a friends house for nothing as a one off and stupidly decided to clean all around the vents for a change. Well it took 3 goes to stop them spotting and a few hours after I went water dripped out of them and spotted again!!!

[dai]

I only do the top of the frames if they are really dirty, you can do over the top of the vents, and at the side of them, just don't let water get up into them.
If I do have to do the top frame , I don't let the water run until the brush is on the plastic, you don't have to have the water running constantly, you can scrub with a wet brush and rinse from above after.
When using the backpack, you can actually save a lot on water by selecting no 4 setting. One squirt of water onto the glass, stop the flow, give a good scrub, and turn the flow on again to rinse.
Believe me the results are just as good, but you need the higher flow rate to rinse.