For the Gundam, no problem for the build. Some really small pieces but it's common for an RG kit. The complete inner frame system (with soft plastic) make the junctions a bit fragile but it's ok for this kit : like many RG, you must take care of them and move the arms and legs with caution (they do not break all that easily, they are not made of paper).
For the build booster (backpack), the build is more "meh" : wings are too thin to my taste and the whole thing is a bit wobbly. But it stays in place.
Fun build, great design : i like a lot !