This is straight off their website:
To be clear, the link to the discounted set is not a Tekton web site
www.runnings.com
The price is $45. This is the link to Tekton for $90
Includes: 5/32-9/16 inch (SAE), 4-14 mm (Metric) 6-point standard and deep sockets, ratchet, extensions, magnetic hex bit holder, u-joint, spinner handle, and case. No skipped sizes. SKT05303.
www.tekton.com
This includes 15mm standard and deep. and the included driver is their "high-torque" whereas the other set has the hard handle.
Both include 5/32-9/16" and 4-14mm (standard and deep 6 point sockets), universal joint, 3" and 6" extension, and a magnetic hex bit holder (but no bits are included).
If you need the 15mm you want the currently out of stock $90 version from Tekton with free shipping and they will add $9 to your account towards future purchases so if shipping is $20 there is an $11 difference if you will make a future purchase. If not, well, buy a few extras from from Runnings like add the 3/8" set to get that 15mm

They claim that their set is 47-piece and Tekton claims 46 and I do not see a difference. They must be counting the case (Tekton does not).