I prefer a stylus to fingers, but these new "pressure sensitive" styluses don't hit the right spot most of the time. Of course, I'm using it on my iPod Touch, whose small size might have something to do with it...
OK, you cannot use an iOS device with a pressure sensitive stylus, unless it's an active electronic stylus - that is to say one with batteries and a data connection of some kind to the device (Bluetooth, plugged into the headphone jack, ect)
A non-powered non-capacitive stylus cannot interface with an iOS Screen, as their screens only accept capacitive touch, and capacitive touch technology cannot be pressure sensitive.
So either you're highly mistaken, are being sold a scam, or are using something bizarre. Sorry.
And I'm not picking on iOS either - this holds true for Windows phones and 99% of android phones as well - in fact it holds true for Pretty much all devices with a capacitive touch screen, unless they have an added physical component inside the screen, which is rare and expensive and usually sourced from Wacom.