Just beacause BDB retails over $1,500, it should in no way be considered a prosumer level machine. I do not think Breville makes that claim anyways...

If you are looking for 2.2 lbs bag of Italian beans, roasted within the last few months, I recommend checking out https://www.cerinicoffee.com/. I have ordered several times from them but you will need to pay for shipping unless your order is substantial. Their best selling beans is my favorite too with hazelnut notes...

I have owned the Infuser and switched to the double boiler more than 5 years ago. I'd think that the huge swing you are seeing with your shot duration with one click adjustment is due to the grinder you are using. Never had a manual one BUT you may need to spend more and upgrade to a more capable grinder. Also, with Breville machines, the pressure gauge is very helpful. Just aim to keep the needle in the recommended zone during your extraction and do not try to hit the recommended duration exactly rather give yourself a time window like 25-35 seconds. This is what Breville recommends anyways, there are really good tips in their manual BTW...

Napoleon Dynamite reporting from the Internets...