I have it and wear it when I am in for some not-so serious riding on steep or fast tracks - if I ride DH in a bikepark or trails with A-line-ish jumps I wear my Pressure Suit.
The Core Saver is light - which means: it does not really offer any protection for the shoulders, it does offer some "light" protection mainly for the rib cage, kidneys and back - but depending on your built it tends to move around a bit. This is what I found out.
Imho a good but not decent choice for something that does not justify wearing the complete combat gear.
"You don't learn from experience. You learn from reflecting on the experience."
- Kristen Ulmer