Great piece of hardware to use with your Gopro, eliminates most/all of the jerkiness of filming while moving. I bought a backpack strap attachment and wore it facing forwards and had no major issues. The battery life is solid, on its own about 2 hours, if you have a good powerbank it'll probably last you a good 6+ hours. It also keeps your gopro charged, so once it dies, you lose the stabilizer but still have a fully charged gopro.
Caveat: I only used it while walking/hiking, so I can't vouch for how it does at high speeds.
Only 3 negatives:
1) $300 is super pricey for an accessory.
2) When wearing it, the buttons are obscured from view, and a little hard to see (you'll quickly learn to find them by feel.)
3) Its not water resistant, so it can't go everywhere a GoPro goes.