It changed over to the new about the beginning of the month. I too am surprised it took this long for anyone to post about it!
I'm pretty sure having the old one available is a temporary thing, but the new one is nowhere near finished. I'm guessing the old one should be around until the new is at least mostly finished.
I do find it surprising that it is the default already, and not just readily available as a beta. The latter is roughly the process used when the really old site was replaced with the older version of the old site (for those of us that remember). But as Tom says, it is probably to get feedback on the design.
On the 5th I submitted feedback on the site via the "Feedback" tab on the right, and got a reply saying it was appreciated and would be passed on to the developers. It also acknowledged that the new site is a "work in progress". So I would suggest that feedback, if reasonable and in line with what they're trying to do, will be incorporated.
Just to compare / add to the lists above, I mentioned the following (in rough order of priority):
Comparing products / more product feature columns
Sorting options, particularly sorting by lowest price in stock
Seeing the three cheapest stores in the category listing without going to the product, also the number of stores listing a product
I didn't really get into appearance / formatting sorts of details.
Recommended Power Supplies Recommended review sites Why stores shouldn't be removed RAM voltage
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I may occasionally give advice regarding (consumer) law, but it is only my opinion based on my reading – I am not a lawyer.
Romans 3:23; 6:23; 5:8; 10:9-10,13