MG Epyon is probably one of the best from the line. You will definitely enjoy it.
In my humble opinion, the major problem is the wings. You can choose to extend them, which is made possible by a sliding mechanism. Do not use excess force during the process although it is tempting. You will attach all the necessary components on one wing piece if I remember correctly. Personally I would recommend to try the sliding mechanism before completing the wing assembly (i.e. confirm whether the parts slide before putting the other big piece of the wing on top of the complex). This way you will have an understanding in how the actual sliding process works and also provides you a chance to correct any misassembled parts before it is too late.
Another noteworthy point is the weight issue of the wings. You can adjust both wings upward and downward through their respective connector parts. However, these parts deteriorate over time due to the weight they bear. My advice is to find your preferred wing height before gluing another connector cover piece on top of the connector complex .Note that the height of the wings will then be fixed permanently, hence make sure you are completely satisfied before application of the glue.
For anyone who has cats at home - Please to make sure to put Epyon in a cabinet. Although the beam sabre stock can be adjusted 360o , the drawback is that it is very loose. One day when I returned home, I found my Epyon was on the floor. While the main body of Epyon is as solid as a rock, the sabre stock broke into 2 halves. Now, I can no longer adjust the beam sabre.
I would like to also comment on the heat rod. Depending on how many rod pieces you put together, the left arm may suffer a major weight issue like what you can expect from a FA Unicorn - the arm will return to its suspending state shortly after every attempt in flexing the arm. Consider an after-market support stand (those for action figures) if you want to put > 5 pieces on the shield.
Finally articulation-wise, this is my Epyon. Nothing to complain!
If you are interested in also getting a Wing Zero (the one in MG is not exactly what you see in the TV version, but close), this is it looks like putting both MS with Zero system together.