I have a Red Sea 625 that has been running for the last 3 1/2 years and from my experience the tanks are just fine. It was the stand that was the issue. The new stands mitigate all the issues of the past stands. They doubled the number of locking screws and added an aluminum center and wooden side reinforcements. You can download the build manual and see for yourself. The stand needs to be built correctly. The stand needs to be leveled in both length and width and all the feet need to be touching the floor, so you have to go around the whole tank and make sure to lower/raise each foot where the tank will be in it's final position.
Now I did have one issue with my tank stand, about a year after my purchase the right side panel showed a buckle in the lower portion of the panel. I contacted Red Sea and sent in my receipt, detailed images that they requested and their first response was not covered due to not building the stand correctly. We'll after many emails back and forth I finally got Red Sea to accept responsibility and send me a new panel. It took three shipments of panels for me to finally get the right one. First I was sent the wrong version, second shipment was wrong color, third shipment was correct color and correct version. I drained the tank, replaced the panel and added some additional fasteners to ensure it doesn't occur again.
Would I buy another Red Sea, yes!
Footnote: I payed $2200 for the new tank from our local fish store. I see today they are twice that price online, check with your local fish store, they may be able to get it to you at a discount like mine.