What is a potential drawback of using a handheld VHF transceiver inside a vehicle that lacks an externally mounted antenna?
Why A vehicle body is largely metal, so it acts like a shield (a partial Faraday cage) around a handheld radio and its rubber duck antenna. RF has to leak out through the windows and gaps, so both transmitted and received signal strength drop noticeably compared with an antenna mounted outside on the roof or trunk. That is why mobile operators use an external mag-mount or permanently mounted antenna and a short adapter cable to the HT.
Watch out The SWR-based choices are red herrings: the metal body may detune the antenna slightly, but the real, dominant problem is attenuation of the signal by the surrounding metal, not a bandwidth or reflected-power effect.
A car is a metal box. Metal box equals shield. Get the antenna outside the box.