Pros: Reflex deck, quiet.
Cons: Difficult to move up a flight of stairs.
After 3+ years of using a Healthrider S300i treadmill (which I discovered that I should not have been running on), I was in the market for a replacement. The Healthrider had developed NUMEROUS squeaks and rattles, and the walking belt was shot with a new belt running $360 plus installation - OUCH!!!. Add to this the aforementioned fact that I was not supposed to be running on it and the need for new treadmill was obvious.
Upon visiting the local NordicTrack store, the manager asked how I was using my current treadmill (mostly running, which I didn't know I was capable of until I had lost 70 pounds over some three months). I was immediately steered toward the 3100R with the Reflex Deck. After trying this treadmill for about two minutes, I was HOOKED!. The Reflex Deck acts somewhat like a trampoline, propelling your every step and greatly reducing the stress on knees (mine are bad anyway) and ankles.
The built-in programs make it so simple to get a great workout, and now I can actually hear the TV over the treadmill - it is VERY quiet (something which I cannot say about the Healthrider even when it was new). Two other program modes allow you to design your own program and hold them in memory. The heart rate monitor in the handgrips also help in designing your own workout and inform you when you need to speed up or raise the incline.
This particular unit was on sale for $300 off retail, plus another 10% off that price. I would STRONGLY recommend paying for delivery (I didn't and regretted it after muscling it up a flight of stairs) as this thing weighs some 220+ pounds. The "assembly" is easy enough to do by yourself with a pair of pliers or wrench and took about fifteen minutes.