No, tumbled products do not offer the same stain resistance. Many of our Unilock Select products (not all) are manufactured using a proprietary process that forms a higher density paver with surfaces that are extremely hard to permanently stain.
Our measurements are nominal because there can be small variances in dimensions when forming concrete pavers. Our recommendation is to measure several sample pavers and work from those measurements. One way to confirm measurements is to measure an area of the product laid out at a local dealer or Outdoor Idea Center. The dimensions do include spacing tabs but we would not use them as a definitive measurement. Areas can also vary due to installation. The size of an area is also dependent on how tightly the pavers are laid.
Our wall products can been used to build fire pits but our stones are not fire rated. If you choose to build a fire pit with our stones you would need to line it with fire brick to withstand the high heat.