Hi CC,
Welcome to the forum
I do a lot of commercial internal high pole work. Most window cleaners I know think I am pretty good with a pole and squeegee.
I have tried doing residential with a pole but there are a few main problems you will face.
1. runs. residential windows are small and often a small opener is placed above another pane of glass in the frame. You would have to clean then detail to stop the runs before doing the glass below.
2. Detailing - made easier by use of the unger fixi clamp but at a distance quite difficult.
3. Time - traditional pole work is time consuming. Ok its safer than ladders but accuracy / detailing is difficult as your not up close and personal.
4. Angles. wfp lads will tell you that depending on the layout of the garden etc you end up standing all over the place to reach the window, sometimes right under (alley way beside house) it or a long way back from it (over a flower bed) etc. With wfp the brush angle is less important as long as you can scrub and rinse the glass. With a squeegee the angle on the glass is very important if a good result is required.
5. Technique. There are many ways to use a pole to clean a window, its a never ending art form. I have over seven different squeegees from ledgers, to 0 degrees to back flips, to wagtails all which have a very specific job. You can even clean a window with a damp microfibre applicator followed by a microfibre in a fixi clamp but it is very time consuming. Learning which technique suits which window and angle takes years to master. I have been cleaning windows since I was 15 and I am now 40. I love pole work but its still difficult with out concentration.
In summary making money in window cleaning is all about having a competitive price and doing an excellent job every time. In this day and age a traditional pole has its place, and that is where all other methods are deemed unsuitable. Where a ladder would be difficult or unsafe to use, or where it is simply quicker to pole (shop fronts etc). Using a pole for residential work in my experience would not be efficient and you would struggle to earn a good living. You also have to remember that on a freezing cold day in the middle of winter in thick clothing and gloves it would be more difficult again.
In you position I would get a ladder, and learn to use it correctly. Save the money and buy wfp.
If you really dont want to use a ladder get wfp from day one.
Remember, to be a professional window cleaner you need to master a range of skills. I use ladders, poles, and wfp regularly, all have their place and all are necessary tools.
Wfp is not better than traditional ladder work, especially as you cant use wfp indoors on the whole, but it is faster and safer to use for external domestic work. A traditional pole is safer than a ladder but you will struggle to make a living. A ladder when used safely is an excellent tool of the trade.
I hope that waffle helps
Whatever you decide to do - good luck
Kev