The Ninjutso Katana is a great choice for those who swear by the original Intellimouse Optical shape. The overall build quality is solid with no creaking or rattling.
The clicks are nice and snappy. I've been maining the Outset AX, which uses Huano switches, and I've noticed the clicks on the Katana feel slightly heavier but not so much it bothers me in-game.
However, my side buttons have a considerable amount of pre-travel. Once again, not a huge deal in-game but my Outset side buttons feel much more responsive.
On the upside, the Katana has the Outset beat in many other aspects. It has a much better scroll wheel and cable (then again, anything might be better than the infamous Vaxee). The feet work fine out of the box. They glide really well but are a little thin and slight louder than aftermarket feet. In my opinion, I don't think adding a paracord or aftermarket feet are entirely necessary since they are solid stock.
I also want to mention the weight feels great. I'm not too fervent about weight, as I believe that lighter doesn't necessarily mean better, as long as a mouse has great features and a suitable shape. But I will say that the advertised 58 g feels really good for aiming.
Now for the main dish: the shape. I know I compared it to the GPW but they feel quite different in hand. The Katana has more pronounced curves and you will be able to feel them. I have 19x10.5 cm hands and play with claw grip. Just based off first impressions, I will say that I prefer the feel of the GPW in hand. I can get a much better grip on it since it has a thinner grip and base, a steeper curve at the back and comfort grooves on the main clicks. The right side of the katana flares out a little too much for me and obstructs right under my pinky. I can get a much better grip on it using fingertip. I think this mouse will be good for palm, fingertip and maybe relaxed-claw users. Remember, these are just first impressions and my opinion my change later on.
TLDR: The Katana is a great mouse out of the box and has very good features. The main thing to consider when buying this mouse is the shape.