Just my own opinion: Personally, I think every product that markets itself as "theft-proof" is a scam at worst, or provides a completely false sense of security at best.
You don't need "slash-proof" anything. Your #1 anti-theft device/feature already comes pre-installed at birth, between your shoulders, below your hat. Your head.
If your head is in the game, with just a bit of common sense and an awareness of what's going on around you, you are going to be just fine, wherever you go.
If your head is not in the game, no amount of slash-proof straps, RFID-resistant magic fields, or other features, are going to do doodley-squat.
Do not be lulled into a false sense of security thinking special straps, gizmos, and other "features" are going to keep your stuff from getting pinched. Sure - pockets on your pants or on your pack that actually close (with a zipper rather than velcro), and that can be closed with a mini carabiner (aka a "speedlink") or similar small devices (heck, even a safety-pin), that will slow down and deter some thieves a bit (good things to have on a crowded metro platform/car). But don't rely on such things. Most of all, you gotta use your smarts. Keeping your stuff safe is not hard, complicated, or beyond anyone's ability to accomplish.
NEVER leave anything hanging on a post or chair unless it is within your reach, directly in your field of view, and you are never looking away. Don't leave valuables in a hotel room, unless there's a safe.
Just my 2 eurocents.