John_K said:
Another question or two from a newb to this: Why upgrade to the Flex? Does it just have so much more power that it can be used on even the most difficult swirls? Is it a D/A buffer as well?
Also, why is power important, because wouldn't too much power cause burns / buffer marks?
IMO it's a matter of using the correct tool for the job. The "weaker" of these machines weren't designed to polish autopaint; they were designed as finish sanders (primarily for woodworking), which is a completely different situation. The more powerful machines that recently became commonly available were designed for detailing and are simply better suited to that task.
More power (or, in the case of the Flex 3401, power being applied to both the rotation and the orbital motion) makes it a lot easier to get the work done in a timely manner. Make that "in a remotely timely manner" or even a "feasibly timely manner".
With a very gentle approach (e.g., PC/6" pads), it's not uncommon to spend many hours correcting fairly mild marring on hard clear (BTDT), and by "many hours" I don't mean just three or four. How many hours of work do you really want to spend on *one* door?
A more powerful machine can also help break down a product's abrasives in a thorough/proper manner (it's not uncommon for very gentle machines to have issues on very fragile paints because the initial bite of a product can leave "pigtail" scratches which don't come out as the abrasive breaks down), actually making said (more powerful) machine *safer* or at least more likely to give good results.
Yeah, it's possible to burn/damage paint with any polisher, even a (pre-XP) PC. And even the most experienced expert, using the most gentle machine, can have an "oops!". But "possible" and "can" are a LOOONG way from "likely". IMO all these polishers are perfectly safe in the hands of anybody with a modicum of common sense who's willing/able to develop a decent knowledge base, apply some thought, and keep focused on the task at hand. That's not to say that a better knowledge base, above-average sense, and experience aren't beneficial

But if somebody is, uhm.... the sort of person in whose hands any of these polishers is likely to cause problems, then that person has issues far beyond the scope of this thread.
Study the subject before you do anything, consider what you're about to do (how and why), stay focused/pay attention, and deal with anything unexpected right away, and there shouldn't be any problems.