Reviewers say the ProForm 400X makes a lot of tradeoffs to attain its super-budget price, including an unusually small (50" x 17") belt, an underpowered motor and insufficient warranty coverage (only 90 days on most parts and labor). As with other ProForm treadmills in this price range, experts agree that you're better off spending more money on another machine, since you'll likely need to have the ProForm repaired down the road or buy replacement parts.
Considering the large number of similar ProForm treadmills on the market, not all models receive equal attention from reviewers. The ProForm 400X, for example, is discussed by only two sources, TreadmillDoctor.com and Treadmill-Resource-Center.com. However, it's clear that comments about other ProForm budget treadmills apply to the 400X, and vice-versa.
As with the ProForm 350, the Stevenson brothers recommend skipping this model. They give the ProForm 400X low ratings overall, especially for walking area, power, reliability and warranty coverage.
Review: ProForm 400X Review, Clark & Jon Stevenson
According to this site, the ProForm 400X shares all the weaknesses of other budget ProForm treadmills: "weak motors, small belts, and weak warranties." The 400X does come with hand weights below the console for power walking.
Review: ProForm Treadmills, Editors of Treadmill-Resource-Center.com