Not everyone has issues with the stock servo, I did because I keep cartwheeling on the roller coaster course the locals call a track.

Some swear by the HPI metal gear upgrade which wasn't available when I purchased a Rhino Digi 4 by Multiplex.

The servo is a direct drop in with existing HPI mounts which come in your buggy box. Aluminium case, metal gears, fastest, strongest and ugliest servo available that fits this buggy.

$109.00 a Tower hobbies and never look back. I Used the stock Hitec servo arm, some say it doesn't fit, mine does and since Hitec own Multiplex there may be something there there that is new in that the heads have similar splines

Some also use a Hitec servo (NOT the 805) it will decapitate itself.
Not sure the number but it is similar to and shares some components with Digi4 at a lower price.