probably won't degrade in a landfill
The deal with these kinds of bags, with a small amount of cornstarch added, is apparently that the small amount of biodegradable material causes the bag to fall apart in time. But only in the right conditions, which don't necessarily exist in the landfill. They would fall apart into tiny particles of polypropylene, and they may leave behind a toxic residue if they do fall apart, from the additives in the bags.
The high density polypropylene that's 95% of the bag is what plastic bags are usually made of.
It's probably better to use Biobags or Flushadoo.
These bags might be more durable because than those alternatives because of the synthetic ingredients.

previous user
Have used this product before. Amazon provided a cheaper price than previous sites. Seller gave me prompt service.

Great, and with the ability to tie easily.
I love these bags for a couple reasons: 1 -- They are very economical. 2 -- They are easy to dispose of (the main purpose of a dog bag by the way). 3 -- They fit nicely over my hand-held pooper scooper, so I have the ultimate in Sanitary pickup.
The only down side to this is the low biodegradable aspect. If you get this for environmental reasons, you will not like it. But if you get it for other reasons, it is fantastic.

Not biodegradable
These bags don't meet the requirements for biodegradability as specified by the ASTM6499-99.

Independent lab analysis has indicated that there wasn't even any detectable corn in these bags.

Consider either:

Spike brand "Business Bags" or BioBags.

Won't Get Fooled Again!
I loved these bags until I read the review on Amazon and found out about the high plastic content. I e-mailed the company and they stated: "The material is: 5% biodegradable resin include starch, synthetic polymer, additives, 95% HDP (high density polypropylene). It takes approx. 18 mos for the process to start and a total of approx. 2 years to run full cycle." Basically, these bags are no more biodegradable than your standard plastic shopping bag. This is very misleading advertising.