Overall I think it's a pretty good mouse, and it would probably be a good option for some. Played on 500 and 1000dpi with a QcK, 49.5cm/360. Two main things keep me from using it (and considering it further) over the FK1:
1. I can't drive the mouse very hard. I flick a lot and beat mice up, but for whatever reason I can't get comfortable with this mouse. I move around much slower than with mice like the FK1, G400, G502, EC2, Aurora, etc.
2. The mouse drags a lot (probable contributing factor to 1). I'm accurate short distances and corrections, but when I go for long flicks I'm consistently undershooting. New feet or pad might remedy this, but I don't find the mouse so appealing that I'm willing to work around its flaws.
I think the sensor performs well but I can't really put it through its paces because the mouse itself can't keep up with my playstyle, but it was pretty accurate with no major tracking issues that popped up. I'd like to be able to say something like 3310 > 3059 but I think it'd be unfair because the mouse itself seems to get in the way of me objectively evaluating the sensor in game. So my opinion is FK1 > Rival 100 but not necessarily 3310 > 3059 (though this is just a 3050 propped up to 4000 dpi and made to play nice in Engine3, right?).
The buttons are meh but I might have been able to live with them; I'm not in love with Huanos but I like them better than SS. I feel like the multiple coatings hurt the mouse--I'd much rather them go all rubber or all plastic, and lose the stippling. Side buttons and LOD suck, but they made some good changes with with the scrollwheel and cord, and I like the shape. For $35-40 and a mousepad it's a good deal imo.