I got the Object 777 Version II yesterday. Overall: Fun tank, I'm enjoying it, and it's not bad!
Armor: The armor on this tank is pretty good. Rule#1, always hide that lower plate, it's paper. Aside from that, the upper hull is pretty strong and the turret is very reliable except against accurate enemies, who will shoot your cupolas. The tracks stick out a lot and absorb a lot of shots; try sidescraping.
Mobility: The tank is pretty quick, it's great for getting to heavy/hulldown positions early. Decent acceleration and reaches high speeds okay, it can keep up with many mediums. The turning speed is a bit shitty, so pick clutch braking perk. I outran a T-10 going uphill.
Firepower: The gun has great penetration for tier IX. Aside from that it is kinda bad. Low DPM, derpy accuracy, and kind of dumpy handling. Not great gun depression either. I put a rammer AND vents on this tank to try and speed up that shitty reload as fast as possible, and mitigate the accuracy issues. It reaches 2,250 DPM with both of those, which is usable.
Overall, the 777 is like a 277 but shittier in every way, and down a tier. I have had fun playing it and do recommend.
It also looks really cool! It has a big turbine ventilator on the engine deck that looks neat, and the cute AA machine gun pod.