So the LTC3525 board turned up today and I've been doing some power testing. Running the basic board from a CR2032 battery doing only limited advertising (every ~5 seconds), the board consumes 28uA on average.  If we run the battery through the LTC3525 so we have 3.3v for any potential peripheral devices, the average is 57uA; twice as much (see the photo below). Not great. I probably need to use the shutdown feature of the chip to switch over to pure battery power when sleeping (perhaps make this configurable on my boards) to reduce power some more. Not clear the test LTC3525 board makes this easy :-(