I've definitely been sleeping on the Shift. I've had a Shift 300 in my bags for probably 5 weeks and finally got around to hitting with it. It belongs to a friend of mine, he is using the Shift Pro (which I also tested today), so he loaned it to me - I've been trying to find a more modern racket to add to my bag.
The racket felt ridiculously light, almost like swinging a light or team racket, but with a lot more power. I had to check twice to make sure it wasn't the 99L. It was a spin monster for me, I don't think I've generated that much spin, ever. It had a high launch angle, but I had trouble dialing it down, struggling a little when I would try to flatten out my shots. I would say that the racket was originally strung in the high 50s, but I usually get mine at 48-50#. The racket also didn't seem very stable against heavier balls, and I was getting this residual vibration from the racket. It wasn't an uncomfortable feeling, more like a heavy + slow short duration vibration.
I also picked up the Shift Pro, and it too felt ridiculously light to swing, despite having a much higher average swing weight. I am currently using a TI.Radical w/ a leather grip, which I've felt a bit sluggish with lately (thinking of replacing it with a synthetic grip as I build back up my strength after a long layoff), but with the Shift Pro I felt like I could swing it for days w/o getting fatigued. The Pro eliminated the stability issues, as expected. And it did not have that residual vibration effect from the 300.
I think I prefer the 300 a little more than the Pro, I really like that it is "under spec" compared to other similar rackets to allow for that customization. I'm thinking restringing w/ my preferred tension and playing around w/ a bit of lead for stability will be my next test for this.