To answer some of your questions. The reason Digicool uses a 200psi transducer is because it is more accurate that way. When you look at the specs of different DRSA's they give you an accuracy. That is over the full scale of the transducer. So a 200psi transducer is more accurate than say a 500psi one.
It flashes to let you know your over the pressure the transducer is capable of reading. This way your not actually using what its telling you for troubleshooting. THis is NO different the the Retard scale on a regular bourdon tube gauge..
If you need to verify standing pressure use the High side gauge... They should be reading the same pressure.. You can buy the hoses with inline ball valves like me to make that easier..
If you are pressure testing a system use the high side transducer if you want to test above 200psi.. With the 1 psi bar graph it is still way more accurate and easy to see a leak then analogs.. But if you can keep it in the 175 range which I suppose most of us do its really easy to see a 1/4 or 1/2 psi drop on that bar graph..
Finally if your low side of a system is running 200+ psi with R410a you have bigger problems then a flashing DRSA...