A negative of surge brakes on a trailer that does not apply to dollies is backing up a hill, which can be less convenient with surge versus electric brakes. This is not a comparable issue with dollies since they are not backed up a hill under load.
P.S. — Talking of dollies, I saw my first ever Jeep Wrangler on a dolly yesterday. It was a rental dolly so likely that Jeep owner had not set it up for flat towing. It was quite stable at well over 70 MPH when he passed me.
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