As Jeff says, there is a huge learning curve, I rarely do a job that is sub-standard, and I say rarely because now and again you will come across a job that you just cannot get perfect.
In any one day thee will always be a window or two here and there that won't be as good as it would if done trad.
By and large WFP is more thorough, it can be much quicker, it is far safer and as well as extending your working life, it will also extend your working day, you are less tired and able to work longer without being so knackered.
How good you are depends on you the individual.
The big companies have many window cleaners, they are not really monitored.
A few months ago I saw one of them doing our local police station..doing it trad off ladders, done an awful job and as for health and safety!
Same company are now doing it WFP, checked their work...awful
Don't blame the tools used! It's the tool using them you should blame!
Ian