I got the regular boot and think it was definitely a good idea. Helps to keep it clean and make it even more durable. I thought about getting the magnet one, but have never really needed it. But if you want to stick it to something metal you may need it. Just depends on how you will use it.
You are right. The black one with the flames is the fastest of all Thermapens. I don't even use a case accessory for mine. I just keep it in the drawer with the rest of my stuff.
magnetic boot is awesome. especially for comps, i stick to a leg of our ez-up and it's easy to fine (glows). Only problem is you won't see those flames, it's translucent.