A first impression for the SubPac M2 I posted on another international forum.
Just finished a 2 hours session with a few different experiences: listening to music on Spotify, playing traditional PC games and VR, and watching movies.
Played a couple of EDM tracks and bass-heavy ones like Daft Punk, thoroughly enjoyable, and you really feel like you're right next to a speaker, albeit with your back to it.
Played "Raw Data", "AudioShield" and "Space Pirate Trainer" on VR with the SubPac M2. Every weapon shots in "Raw Data" and "Space Pirate Trainer" registers unique "thumps" and even on SPT, changing to different weapons from continuous shots to single laset blasts registers its own unique physical signature on the M2 as well. On "Audioshield", combining VR gameplay with music ala Dance Dance Revolution, makes the whole experience more immersive.
Played "Doom". There is a specific level in the "Doom" game called "Kadingir Sanctum" and I swear to God, the amount of LFE in that level is off the charts! I was even gleefully opening up my weapon wheel and fire shots after shots to "feel" how each and every weapon differentiates itself based on how the M2 presents it while firing. Brilliant! The Gauss Cannon nearly blew my back off with its "charge and release"!
Played a couple of movies with heavy firefights, shots and explosions. Registers them accurately and nicely as well. Not a D-Box, 4D theatre, blow-you-off-your-seat kinda experience but enough to make the whole movie watching experience more engaging.
There's a couple of pros and cons. The wires coming out of the breakout box is cumbersome to me, I had to do some "cable management" to make things look and feel near, but I figure I probably need to get shorter cables so that this spaghetti of wires doesnt get tangled everywhere. The breakout box has a clip at the back that hooks to either the strap on the SubPac or your belt/pants. I was wearing sweat pants while playing VR games, and because of the weight of the breakout box, it may bring your pants down LOL! On belts should be fine. Clipping the breakout box to the SubPac strap would work too, but in VR, the box may get in the way when you move about in VR space with your motion controllers, so clipping it at your waist area is much more ideal. The "Intensity" level of the tactile feedback is very good, even at default, there's plenty enough feedback to be felt, and at anything beyond that, you can almost feel like you're on a massage chair?

Also make sure that the straps are tight around your body, otherwise, while moving vigorously in VR, the level of immersion may be reduced if your SubPac isn't tightly placed on your back.
Other than that, it's a winner to me. It makes the whole VR experience more immersive and engaging. It also has this one other side effect: I caught myself look at the mirror and saw how I look with the SubPac M2 on my back, the HTC Vive on my forehead, and headphones on my head and ears, while I was launching SteamVR with mouse and keyboard, and if I add a proton pack, a beige jumpsuit and a ghost trap, I'd look like a freaking Ghostbuster already. LOL!