Rather than use a BNC to SMA adapter mounted on the HT, it's safer (less strain on the SMA connector) to use an SMA cable assembly having a BNC female or other suitable connector mounted on its far end. This way, the SMA can remain installed on the HT all the time, and any stress placed on connectors occurs on the BNC end of the cable, and not on the HT connector.
SMA is a vastly superior connector to BNC in all ways except mechanically. It is better shielded and maintains impedance better, up into the microwave region. SMA is also a more expensive connector; the manufacturers didn't start using them to save money. SMA is the standard on most small microwave equipment, and has been for many years. It was a logical choice for HT's that provide receive functionality up to 1000 MHz, as many do.
73 de Steve, WB2WIK/6