Great review and thanks for starting a thread on this. I've had mine for six months. In the modern era I've owned two Pro-Jects, a VPI Classic, and then the Prime. Despite employing every tool known to man (short of an oscilloscope), I could never get my Classic to sound right to my ears. I played aroud with alignment using a Mint Protactor, azimuth using a Fosgometer, VTF using multiple digital scales, every anti-skate option and setting, levelling using expensive levels, you get the idea. Too laid back, not enough boogie/propulsiveness. I could get it to sound great with Jazz and female vocals, but not rock or the like. I won't go into all the details of my system, but it is all good stuff, almost all tubed and Benz Glider S LO MC cartridges.
In my system, the Prime was a game changer. I got everything I was previously missing-oomph, slam, imaging, soundstage, hair-raising moments, fun. Part of my solution may have been that at the same time I bought the Prime, I bought my first Soundsmith cartridge, a Zephyr. I have a Benz Glider mounted on a VPI 9T on a restored Thorens TD124 and it sounds great, so I think most of my love for the Prime is attributable to the Prime itself and not just the Zephyr. I am about to add a second 3D arm with a SS MIMC mounted. Can't wait to see what it adds to the mix.
VPI made things a lot easier on the customer with a thumbscrew/knurled knob at the counterweight and the VTA tower makes life easier too. Reaching around the back with tiny inset holes and tiny allen wrenches with the Classic was a royal PITA. Definitely grab a SS Counter-Intuitive., Worth every penny! I am still not in love with the unipivot because it seems to make anything involving horziontal plane changes (azimuth and seemingly/absurdly anti-skate) a bit unsettling. I have also never felt very comfortable with HW's "don't sweat it" approach to set-up; antiquated Shure VTF gauge, aluminum swizzle stick across the headshell method to set azimuth, using a ruler or index card to set VTA/SRA, anti-skate is optional because "I don't believe in it", etc. There is a lot to be said for the common sense approach that it is absurd to sweat over details when much of vinyl reproduction is a compromise but such is a half-truth IMHO.
So what makes the Prime such a great table? Well, in my view the reduced mass plinth speeds up the PRAT (sorry, I realize that's oxymoronic) the outboard motor bleeds vibrations away from the tonearm, the new feet are a big improvement over the mini-HRX feet, and the 3D arm is a HUGE advance in and of itself. I can't envision a bigger bang for the buck table than the Prime. Mine has no visible run-off error in the platter and the fit and finish is flawless. I know I have a table that will last the rest of my life and VPI has always had great customer service if you don't mind just a little patience and perseverence.