Short answer - NEXUS allows even veteran m/kb users to play console shooters with a controller. Whether or not you can slay the lobby depends on time and dedication, but you will be competitive very quickly.
I've been an m/kb gamer since the Commodore 64 and I hate using a controller for shooters. The only shooters I've ever beaten with sticks are Horizon Zero Dawn and the Ratchet & Clank games. Every other console shooter from the last decade I've beaten with a XIM m/kb adapter from one generation or another.
Motion aim makes a huge difference to my controller aim, which is typically nothing short of awful. I am not kidding, I am trash with a controller. The whole reason I landed on XIM in the first place is I kept running out of bullets in Uncharted on PS3.
For single-player games, it'll be quick and easy to adapt to NEXUS from m/kb without the pressure of other players gunning for you. Precision is surprisingly good and motion aim is really stable, depending on your NEXUS settings (calibrate it first). The learning curve is pretty shallow - I recommend disabling Motion Aim for HIP and enabling it for ADS only (the default setting) to get used to it. The most obvious benefit of Motion Aim is recoil control, which is dead easy to do by simply tilting the controller forward. Aim assist is very sticky and smooth - it's in a whole other league than APEX because NEXUS is designed to use it.
For multiplayer online shooters, it's going to take me more time. I'm very hesitant to give up my APEX for MP gaming (really...why would I?), but when I have used NEXUS in MP, I've had roughly the same KDR. I feel less comfortable and confident with a controller given my decades on m/kb, but that's just a matter of putting in the time. Guys like d1sable and MrBrutalFrosty are going to stomp heads with a NEXUS.
NEXUS games require Smart Translators for Motion Aim. As we know, some STs are better than others, so results will vary. Overall, I've really enjoyed that I can finally play a console shooter with a controller. Being pain-free to boot is a massive plus.
I'll be able to demo the difference NEXUS makes to my controller aim by simply toggling motion aim on and off real-time on Twitch. All we need is the green light from OBsIV and a few of the testers will start showcasing NEXUS on Twitch & YouTube.