I'd like to provide my feedback on the Renaisser pen I've got for free, as someone who has went through number of devices over the last few years and have lots of experience testing different pen tech.
Initial pressure required for the pen to start inking: seems on par with the Surface's last pen.
Pressure curve: Renaisser is definately more firm, but that's not exactly a plus in my books, as it requires more force to get to thick lines. Adjusting the pressure curve is limited for the surface line, so it's a matter of personal preference, if you require firmer curve this pen might be a good buy, if you like it soft, the surface would be better.
Jitter: same as surface's pen, interestingly enough not worse, which is a nice bonus, as it's like 40-50 dollars, compared to the Surface pen. But it's definitely not better.
Features: No eraser on the back end was a compromise that was made to make it cheaper, not a fan, as I use it on all devices that I draw on. Also no shortcut button, never used that feature much though, as I'm used to Wacom's passive pens. You have to turn it on each time before using it, by tapping it's side button. Both magnetically stick to the device. Renaisser is charged via USB, which is a concern for me, as if the battery dies in a couple years, so does the pen.
Comfort: Plus is that it's way lighter than the surface pen, similar to a pencil, Shape is similar, though it's abit thin. As far as balance goes it's not as top(back end) heavy as the surface's pen, but the shape has weird texture that makes it rougher, so it's less slippery. The pen button similar to the Surface pen is hard to click.
Pen hover: slight lag, but hardly noticeable, also the prediction algorithm surface uses on it's UWP apps doesn't work on this pen, this functionality is not used by most serious drawing apps (Photoshop/Clip Studio and more) so it's not really important to me.
Nib feel: the default rubber nib feels the same as the one on the surface pen. The plastic ones are kinda meh. Too thin and feel worse than the default rubber one, and you get two of these. Too plasticy, the Surface's plastic option(in the tips kit) at least improves the tilt/stability of the pen.
The positives are: no added jitter(compared to surface), it's lighter and more balanced, no noticeable added lag, activation force is same as the Surface pen. 20%-40% cheaper
Negatives: Pressure curve feels way too firm(can be adjusted, but not fully), you have to constantly turn the pen on, no eraser, no Bluetooth functionality. Pen is abit too thin. Battery can't be replaced if it dies(usb rechargeable)