I bought this jar to replace the original jar. I spoke with a CSA to try to understand why this might be a better choice for my smoothies over just replacing my jar with the original design. I would agree that this jar does have a stronger blade and because I use frozen fruit I feel this is a plus but I'm not sure yet about the 5th side.
I had the original jar bought over a decade ago finally blow the seal out, so did the upgrade. The wider base makes it much easier to clean, and yes, the fifth wall somehow makes the flow in the jar not create dead spots.
Very happy with our product and when we needed a replacement part it was easy and reasonably priced and delivered quickly. Would definitely buy more blendtec products