Before there was SPD the clipless system of choice was the CycleBinding pedal and shoe combination that had a large protruding cleat which made walking in them near impossible.
With the launch of their SPD pedals and cleats Shimano revolutionized clipless pedals. Thanks to their small size, SPD cleats could be fitted in a recess in the sole, making it possible to walk and paving the way for clipless mountain bike shoes and pedals as we know them today.
Since 1990 the basic idea has stayed the same, but advances in materials has made the quest for lighter but stronger designs possible. Their Trail range of pedals add a platform or "cage" around the standard pedal to increase the pedaling platform. The extra platform helps, when it's wet or muddy out, to ensure your shoe does not slip off the pedeal when trying to clip in. This is especially true for trail riders who unclip every so often to get a foot out or for riders who need to get a foot down through sketchy sections.
The XT Trail pedal fits in below the top tier XTR Trail, but both share the same SPD mechanism and dual-sided entry. The XT's bodies are slightly thicker and they spin on solid axles as opposed to the hollow units on the pricier XTR Trails. Ease of entry and release can be adjusted via a 3mm hex wrench. Note that having it too soft or easy can lead to accidental unclipping on the trail through rocky or rooty sections. The cage features chamfered edges to lower the chances of pedal strikes and deflect the blown when it does happen.
On the Trail
What sets the Trail pedal apart from the standard range is the extra platform - other than that they are exactly the same as the standard XT pedal. If you're using shoes with a stiff carbon sole chances are you won't really feel the extra platform under foot when standing or pedaling along. It is more evident if you ride in shoes with a more flexible sole like Shimano's AM range, Giro Chamber or Five Ten Impact. Although not exactly comfortable to stand on for long periods while wearing very flexible shoes they won't tire you or cause pins and needles.
As a longtime flat pedalm, user I found these more forgiving when trying to clip back in and the extra size did give me peace of mind going through rough stuff.
There is good reason why XT pedals set the benchmark for durability, ease of use and features and they are competitively priced. The trail version adds extra versatility by offering a bigger platform with all the features you have come to expect from Shimano pedals. This particular pair have been doing duty on and off on a variety of bikes over the last 12 months and they are still creak and play free, and the cleats still engage first time. Both the pedals and cleats are showing little sign of wear, although there some rock-strike battle scars.