Your electrician is correct. You 100% need to do this. No there are no negatives.
The updated 2020 version of the National Electric Code requires whole house surge suppressors. Keep in mind that they also recommend you use surge suppressors at the point of use for sensitive electronics (i.e. anything more delicate than your stove or dryer).
The house suppressors clamp high, from around 400V, while Furman or TrippLite have models that clamp < 200V.