I can't answer your SDRPlay questions... 

Just be aware there are 3 current versions of the MFJ-1708...   The base 1708 is a true T/R Switch for old boat anchor rigs...  I don't think you want that version... 

The two newer ones let the transceiver and the SDR share the same antenna during receive...  So there is a 3 dB loss as two 50-ohm radios are connected to the antenna at the same time...  Think of it as a Tee Connector during receive...  During Transmit the transceiver is connected to the antenna and the input to the SDR is shorted to ground to protect the SDR's front end...

73 Dallas N4DDM