James, welcome to Coffee Snobs (your salvation from bad/mediocre coffee).
Youll get a lot more replies soon so let me briefly answer a few of your questions.
I dont know the Breville 800 so will leave comments to others to compare to a thermoblock unit.
"Amazing difference" - yes - never return to the dark side.
800ES - others will comment.
BG450 - NO! - Sunbeam EM450 is a minimum.
Is roasting with a popper that simple? - Yes!
Soggy pucks - probably the fault of the stale supermarket coffee and possibly pressurised baskets in your Breville.
Enjoy the journey.