I had old foam mats that I replaced with these. I did the research with other mats and was placing an order through a professional online mat company. When the guy told me the shipping cost, I was shocked. The freight cost was more then the mats I was buying. More research and came across these. Great choice for what I do (P90X stuff. No weights on the mat,) After I installed (on a concrete basement floor) I did a little workout to test. Still a great choice. Good cushion.
When I opened the mats, there were packaging marks on them. No issue after cleaning. A few seem darker then others. I think they have lines on the design, saw that after, so you may want those to go in one direction.
My advice for install: After cleaning the floor, lay them out upside down and lock them together. Use a rubber mallet to bang all the joints so they're flush. Some will still stick out a little but no worries. With two rolls of carpet tape, tape it all together as per the instructions on the roll. With the extra left over, tape some of the joints. Get someone to help flip it over. Try to keep it centered. It's tricky but it works. Use the mallet again. Clean the tiles with water. They do smell some, but it should go away. Just get on it and sweat! Great mats for the price.