In 10 years of playing airsoft, including 5 of being an airsoft mechanic, I've never, ever seen a stock BBU fail.
So if you're planning on changing it for durability... just don't. There's no point on doing that, as the stock one will last forever.
Aftermarket BBUs are meant either to provide slightly faster cycling at the expense of lighter recoil (light weight BBUs such as the three you linked to) or to increase recoil by having a wider nozzle and seal, heavier weight and other means, such as Volante's
So if you're planning on changing it for durability... just don't. There's no point on doing that, as the stock one will last forever.
Aftermarket BBUs are meant either to provide slightly faster cycling at the expense of lighter recoil (light weight BBUs such as the three you linked to) or to increase recoil by having a wider nozzle and seal, heavier weight and other means, such as Volante's
