The only reason for 4 stars is that the vinyl upholstery seems a bit cheap and I worry that it will rip or wrinkle easily. I guess I didn't read the description well enough because I thought the seats were fabric. All in all, for the price, these are nice chairs. I will give them 5 stars for comfort and my mother loves that they are not very heavy. She is 84 and she didn't want chairs that were too heavy to pull in and out. 
As far as assembly, get some good gloves or invest in an allen wrench or allen key kit that has more than a 1" "torque" handle. By the time I finished assembling all 4 chairs, my hands were in pain because the end of the allen wrench cuts into your palm with every turn of the wrench. I found a longer handled wrench in my tool box after I had already assembled these and I was able to tighten everything much better.  I think the people who are saying that the bolts come loose are just not tightening them enough, which is hard to do with the tool they provide.