I don't know anything about the bicycles that you are trying to decide on buying but here is what I suggest.

Once you decide on the bike you want to buy from Walmart or wherever, buy it and then take it to a bike shop you trust. I say this because many big-box stores place more attention on the fact that they just put them together and get them out the door, no matter what consequences may happen to the people who buy them. If you have someone you trust check your purchase, these possible problems can be nipped in the bud.

Good luck and good riding.