can't find a review for the 450W, but the 550, 650, 750W units of the Edison series is definitely a Seasonic G, I assume the 450 is as well
as for your question:
Gold/Silver/bronze tells you about efficiency. this means how much power is converted to heat and how efficient the PSU is working.
for example there were PSUs that could output 450W but draw 600W from the wall. and when you only drew 300W it still took 600W from the power outlet, got hot (and mostly defective after a time because of the heat but at least hurt your electricity bill)
that's why back in the day there was the 80+ label that set a standard as to how much power a PSU is allowed to waste at 20%, 50%, 100% load.
later on this label was expanded into bronze / silver / gold and later platinum & titanium
generally the difference between a bronze and a platinum PSU below 1000W is truly insignificant in terms of energy consumption.
did the calculations once based on a 550W unit (gold vs. bronze) and you needed 6-8 years of usage to justify the 30$ the gold unit cost more or something like that
anyway, there is usually a big quality difference between units that got a 80+ rating and units that don't, at least I don't know any halfway decent PSU that's not 80+ rated at least
but if it's bronze/silver/gold says nothing about the quality.
it's like saying a cheap chinese car is better than a Benz because you get 50miles further with a gallon of oil.
yes, the chinese car might have a more efficient engine but it says nothing about the build quality of a car and frankly it won't matter if you get 50km further if the car doesn't start anymore after refuelling or starts to burn down.
it's the same with PSUs.
sadly advertisement says "450W GOLD" -- which means exactly nothing.
it could be a 450W PSU that can only deliver 275W in a real world situation and is likely to burn your house down when under load.
like with cars, there are some parameters that help. like if you're buying a Benz you know that it ain't a bad car. of course some series might be a bit better than others but generally you know you buy trusted quality.
same applies to some PSU manufacturers, like Seasonic or in the last few years Super Flower. if you get a PSU that's made by them, you know you'll end up with a quality unit.
then there are manufacturers like FSP or Delta that are a bit hit or miss. a few of their units are really good, others are mediocre and some are just plain junk.
the thing with PSUs also is -- to make it a bit more complicated -- that you for example don't see a lot of Super Flower or Delta units running under their own name other companies buy their designs and rebrand them.
Fractal Design for example got the Integra M and the Edison M series.
Fractal Design doesn't build any of them though.
they buy a certain mediocre FSP design, attach their own casing, fan and box and sell it as "Fractal Design Integra M"
while they buy a pretty nice Seasonic design, attach their own casing, fan and box and sell it as "Fractal Desing Edison M"
someone who doesn't know and doesn't look into it just sees 2 PSUs, both from Fractal Design, both 450W, but one costs 20$ more, so he buys the cheaper one and thinks he got a good deal. well. he doesn't.
as to why is one better than the other:
it's mainly due to the parts used. you can buy a shelf at IKEA that will look used and cheap the moment you've assembled it due to the low grade press board and cheap paint or you can get a shelf from a carpenter made out of solid high grade wood, oiled and painted with maybe even organic materials that can last generations.
as for PSUs, there's the interial design (do they use a simple and easy design like an IKEA shelf that any middleschool-dropout can assemble or a more sophisticated delivery that's safer and cleaner), the capacitors used (are they japanese premium capacitors that are sufficient to handle unstable power conditions, high currents and can perform even when getting a little hot, or are those cheap chinese/taiwanese caps that work just fine as long as they're in perfect lab conditions), the soldering quality and of course the different protections implemented, like the PSU automatically shutting down when the voltage rises to high or drops too low, shutting down when it detects a surge, when it overheats and so on. cheaper PSUs implement not all of them or not properly which can lead to a unit failure. depending on the design and quality a unit failure can lead to different outcomes. for example your power line is hit by lightening. a quality unit will trigger several protections. It might be that the PSU fries and won't start anymore or that it works just fine after cooling down. either way, your computer is save.
with a PSU of questionable quality the unit won't protect your computer and won't sacrifice itself but would go out, taking your CPU, board, GPU with it and in the worst case catch even fire.
TL,DR:
better parts used in the PSU make for saver, cleaner and longer power delivery to your system for a little higher price
it's generally the part most important not to "save cash" on.
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