The BM1 and the BM1 Compact are very similar, they both tell you Gross metering like 99% of all battery monitors on the market, so if you have solar pumping in at 10 amps, your three way fridge on 12volt drawing 15 amps and lights drawing 2 amps your gross metering will be at a minus of 7 amps. the BM1 i believe is the easiest to wire and easiest to use on the market. The only difference is the the BM1 has Amp hours consumed. they both display State of Charge, Amps, Volts and Time to go at current rate of discharge.
I am the distributor of the products in Australia, I have also sold all of the other brands and models available, finding the NASA Marine gauges to be easiest for use and installation as well as at a glance with out pressing buttons it shows you loads of information on your battery health.
I cannot match the price of overseas internet sellers, as I do have to pay, Duty, freight and make it worth my time and effort to make a few dollars but at the same time I warrant all products that are sold through the business into Australia.