Yes,
It has four settings.
Setting one gives a 'dribble', setting two is the 'normal setting' for window cleaning, setting three 'spurts out' but I only use this for three-storey stuff, and setting four is a waste.
The button to change the settings is situated at the base of the backpack; which - to begin with - is a bit of a pain; especially if you wear gloves all the time; like I do.
But like anything, you 'get the knack' of it, and even wearing thick rubber omnipole gloves, I always get the button first time.
To switch the backpack on you press the button twice, to switch it off you push it three times. Occassionally, one of your 'quick button presses' doesn't register and you have pure-water flying all over the place.
Pushing the button all these times sounds harder work than it is. It's not.
I mount my backpack on a sack truck, which I've hacksawed some of the metal away to give my fingers easier access to the small button.
I've also drilled some holes and placed a couple of bolts with nuts, in the bottom of the sack truck to raise the base a couple of inches from the ground, so I can get my fingers in.
(I can take some photos of the backpack and trolley if I'm not clear; and will if you force me to).
I'm not saying the backpack is always the best option. But it probably is you've a residential round with some areas of difficult access and work from a car.
It's all well and good some people saying stick a 125 litre tank in your car and stuff, but if it's the family car, then you've problems. Strapping the kids on the roof rack isn't the best way to transport them about.
The Shurflo backpack is a great starting point and a good way to 'dip your toe' into the world of WFP.
Remember, some lads here think van-mounted systems are the best and haven't used their backpacks in months. Others say they only use their backpacks and rarely use their van-mounted systems.
If you do find the backpack to be unsuitable, it's going to be a cheaper mistake than what you possibly could make.
----------------------
Thanks Leeksons, for saying in twenty-words, what I've said in hundreds!