1.) Does the rubber reek?
These days, with homes being so well insulated, a strong rubber smell in your building is probably going to get circulated by your furnace or air conditioner over and over throughout your home or business. In the old days, homes were so poorly insulated that, eventually, the smell would dissipate over time as the air turned over. That's not the case today. If you have a newer home and a stinky floor, you'll be bumming for a while.
1a.) It DOESN'T MATTER if the rubber is virgin or recycled. The binding agent is the critical factor
Rubber is heavy. That means it's expensive to ship because freight companies usually charge by weight. For your home gym, chances are you can get by with an 8mm rubber product. This is thick enough for day-to-day abuse that comes in most gym environments. While the standard used to be 3/8", most people are opting for 8mm. It is roughly 1mm thinner than 3/8". From a performance standpoint, you won't know the difference. From a cost perspective, you most assuredly will.
4.) Rubber flooring is NOT good for a garage as a general rule. This is because rubber tires + rubber floor = shredded rubber floor.