Penetrator basically a mobile version of Annihilator. It is equipped with a tremendously powerful long range tachyon accelerator, which can one-shoot most T2 bots and even deal with lighter T3. However it is costly and very fragile.
Never send them alone to the front. Always keep them spread as they explode vigorously and may start chaining.
To aim properly, they need good vision. You can use Gremlins or a scout spam to provide it. Their aim can be also hugely improved with use of a Targeting Facility. Important: they uniquely have an ability to reverse, which is useful as they can only shoot forwards and their turning takes forever.