I have experience with this exact rifle, owned by a friend. Aside from the motor, it's fairly solid.
Unfortunately the motor is so weak you can spin the pinion like a top, and they pair it with 22:1 gears, which are quite slow. This leads to horrible trigger response and sound.
The barrel is aluminum, and holds the accuracy back, but i flathopped the stock rubber, which was nice and soft, providing good airseal, and it shoots amazingly well for the amount of work.
i switched the motor to a Krytac 30K I had lying around and changed the gear ratio to 18:1. The stock gears are actually decent and were shimmed perfectly, but JUST SO SLOW. Since I wasn't adding a high-speed motor, as this was a budget rebuild, the gears needed to go.
Bushings are really nice actually.
Piston is FMR and very sturdy.
cylinder and cylinder head were aluminum and sealed nicely.
piston head sealed nicely.
I replaced the nozzle since my buddy's was worn for some reason. This was actually the only internal part with any wear on it.
gearbox shell is almost identical to a G&G EBB shell--no gripes.
Hop unit was fine.
Trigger unit got finicky after a while. i replaced the trolley with a Krytac spare and it works great.
Overall, the motor is what holds this back. For the price, Arcturus is far superior. Actually, i even like those $100 Cyma M4s better, since those will do 20 RPS on an 11.1v and sound pretty nice while doing it.
Aside from motor and barrel, I'd keep it stock.