Similar experience here with the 62mm version, I just don't trust it much at the moment.
My review of the Yuxin Blue
So it took me nearly TWO HOURS to reassemble the cube. It's a long time since I've reassembled a 4x4, and getting the first 3 combined internal edge pieces to stay in was a nightmare. There's even less room inside the cube then there was in my Weisu, and I set the tensions pretty tight, which gave me very little room for flexing the internal centres to fit the internal edges in. Also I should've finished a corner before moving on, I tried to insert a 4th internal edge, should've done 2, then built the corner, then a 3rd.
In retrospect, looser tensions, less ambition. More haste, less speed(cyoobin)?
BUT, once lubed and correctly assembled, and with the Fangshi springs, it's AWESOME. Does it lock up? Yes, a little, but probably because I can't turn a 4x4 properly. Most of my lockups are at the 3x3 on 4x4 stage, so I did some 3x3 on 4x4 averages (per my previous post, I'm a noob at 4x4, so this is the stage where I can honestly tell if the cube is holding me back).
I did an Ao12 on my Weisu, which was 34.12.
I did an Ao12 on my Yuxin, which was 26.77 (best 22.53, used my phone timer, but lower variance probably than my 3x3 solves - will put this to the test with CSTimer tomorrow)
I was averaging about 2:40-2:50 with my Weisu. With no additional practice (just picked it up and solved it a few times, my rolling Ao12 is down to 2:36, with my last solve on the Weisu being 3:09.141, followed by a 2:20.003 and a 2:11.756 on the Yuxin. The 2:20 had double parity; the 2:11 had PLL parity.
I was partaking in the race to sub-30 in 3x3 on 4x4 to get faster turning on 4x4, and I'm pretty sure I'll graduate from that immediately. I was also taking part in race to 2:30 on 4x4, so I'm pretty sure I'll be getting past that landmark fairly soon as well. I'm confident will be sub-2 using this cube in no time whatsoever. Possibly later this week!
So it's 60mm, which may account for a bit of the speed increase, and also stickerless, which the WCA now say doesn't help... so... but it's pretty! It's also significantly quieter than the Weisu, even having only been solved about 5 times. Turning feels very smooth indeed. I have the tensions a LITTLE looser than my Weisu, but it feels infinitely MORE controllable (go figure). I'd imagine it's because everything internally fits together so tightly.
Sadly it exploded internally before I could judge whether the spring swap was worthwhile. I won't be taking it apart to swap the springs back in a hurry. With the new springs, lube, tensioned to avoid more pops, it's STREETS ahead of the Weisu. But who uses a Weisu anymore? Would I recommend it over a 2-year-old 4x4? Unsurprisingly, yes! Is this, therefore, the most pointless review ever? Yes!
Sorry for wasting your time. I'll be sticking with this cube until I'm sub-xx, or it starts to pop lots and makes me cry. Initial outlook, however, is good.