[nigelpritchard]

Many thanks for the inputs so far.

Have now determined by use of my NanoVNA that it is quite respectable as a RF load up to at least 500MHz, with VSWR = ~1.05 over the range of 100-500MHz, and the minimum being at 432MHz (1.02). From about 550MHz VSWR is then rising to 1.08.

Now need to understand how it performs in the actual power measurement domain.