Okay, finally got this figure for myself and I'm enjoying a whole lot. The Siege UM that I first saw was mistransformed by its owner leaving a gap in the top deck that I thought was a flaw of the toy, but having transformed it correctly myself I can see that there is no gap. To be honest, most of the drawbacks of this toy are pretty understandable and easily forgivable.
e.g. Ultra Magnus' armour head is not concealed but rather dangles from the trailer ceiling, but honestly there's not much else you can do the cover it up. I prefer to just spin it 180° to cover the face. It's not nearly as bad as Energon Ironhide whose head sits atop the vehicle for no apparent reason and you know that they really could've easily done something to conceal it.
There's just one flaw in this toy that I think could've been avoided or done better, and that's the angle of the feet on the armoured robot mode. The feet tilt inwards which looks fine when the robot has its feet apart at just the right width, but otherwise it looks weird, especially if the robot is just standing normally with the legs together. It also makes the rear of the trailer look weird. The feet are able to tilt inwards but not outwards so it cannot be corrected. They should've either given the feet the ability to tilt outwards (enough to straighten them) or just hard mould them in a neutral straight position. The thing is, the inner cab robot has full ankle tilts. I would've preferred to see the armoured robot given better ankle tilts and sacrificed the ankle tilt on the cab robot.
I'm not a fan of the battle damage so I tried to remove it. Managed to get most of it off. Be careful with the red tummy panel as it is white plastic that's painted red. I accidentally faded a small portion of the panel (which isn't visible in robot mode and only forms part of the top deck in truck mode, so it's not devastating) despite being careful. Might be best to cover it with masking tape.
PICS
Armoured robot mode
https://i.ibb.co/zH99YpH/SIEGE-ultramagnus02.jpg
See how silly the feet look when you don't have the legs apart at exactly the right width?
https://i.ibb.co/ZM58cSp/SIEGE-ultramagnus03.jpg
While the ankle tilt on the cab robot is nice, I could've done without if it meant giving better ankle tilts to the armour.
https://i.ibb.co/XYNzmSg/SIEGE-ultramagnus04.jpg
https://i.ibb.co/nBhs6nL/SIEGE-ultramagnus05.jpg
Truck cab
https://i.ibb.co/tHJX0yJ/SIEGE-ultramagnus06.jpg
Rear view - like a Cosplayer
https://i.ibb.co/tHDGDK5/SIEGE-ultramagnus07.jpg
Truck mode - upper deck
https://i.ibb.co/Z8fqymg/SIEGE-ultramagnus08.jpg
Front view
https://i.ibb.co/CJZCL75/SIEGE-ultramagnus09.jpg
Rear view - again, not a fan of the permanently inward tilting feet
https://i.ibb.co/zQqSMqq/SIEGE-ultramagnus10.jpg
After attempting to strip off the battle damage decos
https://i.ibb.co/TM8tDsh/SIEGE-ultramagnus11.jpg
https://i.ibb.co/vzyb3Kd/SIEGE-ultramagnus19.jpg
Cleaned up cab robot
https://i.ibb.co/WFb9pJJ/SIEGE-ultramagnus12.jpg
G1 comparison
https://i.ibb.co/ZMkbcpW/SIEGE-ultramagnus13.jpg
https://i.ibb.co/QQYS3bb/SIEGE-ultramagnus14.jpg
Ah, the joys of the 5mm gun post :)
https://i.ibb.co/gWHhs0G/SIEGE-ultramagnus15.jpg