Well its not about comparing the circuit design per se. Its not like high end audio where circuit design can have an effect on the sound. more of the the workmanship and quality components.
Here are some tips:
1. Look at the boiler and compare. lead free brass, stainless steel, chrome plated. large stainless steel boilers cost more. apparently less prone to scaling.
2. Group. VBM has done alot of testing with theirs for temp stability. I'm not saying VBM makes the bestest or the most solid group ever but at least you can be assured some testing is done and its not just a copy with some parts shaved off to save costs. Look at the chrome plating too. The group and portafilter will be one of those parts that will experience alot of wear and tear at the mating surfaces. which one is over engineered for structural stability? 1mm of thickness can make a world of difference. for E-61 check out the thermosyphon design. does it overheat at idle (i'm not taking about the HX), or does it maintain stable temps after reaching a good set point?
Is your HX design a dragon, mixer or agnostic? I really feel this is very important to know esp if you want to explore different roasts. If you vendor doesn't know...well then he doesn't know his product very well.
3. pressurestat. some are better than others. tighter dead band and reliability. compare jaeger and sirai and MATER.
4. Chassis. any flex when you lock in the portafiler. how is the boiler and pump mounted on the chassis. Some brands used to have a flexing problem. (alex i think). Vibrations? loose panels? sharp drip trays?
5. Wiring and layout. examine the wiring, soldering. If inside is a total mess then likely the machine is not well made and will present a headache when doing repairs. Are wires directly touching the boilers? Is the power control unit, PIDs and other electronics (volumetric brewing etc etc) isolated far from the boiler? Will there be a problem over time when the electronics are exposed to boiler heat?
6. Are things that you need to adjust easy to access? Do you need to remove all the panels and find some hard to reach screw to turn? or is everything within easy access? (OPV, Rotary pump pressure, pressurestat, pid,) Whether need to adjust or not for new machines wearing in really depends on luck. Some do some don't. My guess is most do. Pressure stat almost definitely. What to adjust depends on what machine you have. settings are likely to drift from default factory settings. if it changes to much eg boiler pressure or brew pressure then its really a good idea to adjust it back to factory settings.
Sure some settings are easily googled. but still very difficult to do, like rancilio silvia opv adjustments to get correct brew pressure...
Circuit design may not affect functionality but can affect longevity of system, stress over time or in the circuit breaker trip due to a surge.
1: how to tell lead free brass?
2: this is hard stuff! How to compare chrome plating? Sound like need to bring a micrometer to measure different parts of machine.
Design of this and that? Which is better? Seller tell u that but if the baby is open and cannot tell the diff and seller said the wrong thing how? BS sales person can talk techie exist out there.
3. This also hard. Ppl need to study and understand this! Put college degree to good use!
http://web.applied.com/base.cfm?page_id=4492
5. Agree messy wiring is a headache come to repair but messy wire does not mean poorly made product. How far away from heat source is recommended, need to pull data sheet to understand each electronic parts heat tolerance behavior!
Just by these few stuff, I felt one already master enough to buy parts and assemble your own machine. No need to buy mass produce ones. This buying experience is intimidating for me if one really study so much and zero down the comparison
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