This is worthy of note: Pens have been the primary tool for interactive work for more than a decade. Other types of pointers go back even earlier. But, fingertips were never one of the tools in the interactive arsenal.
More than a year ago, I saw a DLP.com (Texas Instruments) demonstration at CES where touch was being used instead of a pen. At that point, it was simply a technology demonstration, no products on the market or announced at the time using it if I recall correctly. But TI was making the technology available to those projector manufacturers using DLP chips (for a cost, of course). It was interesting, I played with it, and it worked. Prototype that it was, it wasn't perhaps fast enough or precise enough to be "ready for primetime", but the benefits were obvious.
It wasn't shortly before the Brightlink 585 arrived for review that I got a demonstration of the top of the line Brightlink 595Wi. There are a couple of differences, but the big one is touch interactivity. I got to see two people working the 595Wi simultaneously, each drawing with different colors, using three fingers on one hand, and a pen in the other. That's right, the ability to have eight simultaneous actions to be done. Eight people could be up there (assuming a large enough projection surface to have room for them all to work around the board.) Some could be drawing, others annotating, deleting, or adjusting the menus… Or all eight might be writing 100 times "I will learn to be interactive!"
It really was impressive. The Epson pens work well enough, but I have to admit, I'd rather be able to use a finger. and, with the finger touch, it probably would work with a conventional screen (although that still might not be a great idea - wash your hands first)?
The finger touch ability has several benefits. I think it's more precise, and faster, and it also means you don't have to use a pen, find a pen, etc., which means no opportunity to lose or break a pen. Keep this capability in mind. It will mean spending a bit more on the 595Wi than the 585Wi, but in many cases it may well be worth it.