Compared to road shoes, most mountain bike shoes have more flex in the sole; this is to achieve a comfortable compromise between the maximum power transfer sought after in road shoes, and the ability to walk off the bike that is necessary for off-road riding. As you move towards the higher end of the mountain bike shoe range, you will see more carbon fibre soles; these are designed primarily for mountain bike racers who have a greater focus on power tranfer, so if you think you'll be walking a lot in your shoes, then a pair of plastic or composite soled shoes is a better option.
Mountain bike cleats are very different from road cycling cleats, and the two ranges are not inter-compatible. Mountain biking cleats are smaller to allow them to sit inside the grips and lugs on the sole of the shoe, they affix using just two bolts, and they are designed so that they stay clear of mud and debris. The cleats you use will depend on the pedal system you are using. Cleats are not normally compatible between pedal systems, though for mountain bike shoes they all use a two-bolt mounting system. Please note that cleats are never provided with shoes.
As with road shoes there is a wide spectrum of ventilation levels in mountain biking shoes. At one end there are winter boots, which could be fully waterproof, Gore-Tex lined and have sealing cuffs. At the other end there are summer racing shoes, which have more mesh coverage, less synthetic leather or rubber, and an overall lighter weight
BUCKLES, VELCRO STRAPS OR BOA LACING
The means of fastening your feet into your shoes largely falls down to three options; Ratchet buckles, Velcro straps or BOA cord fastenings. Traditional Velcro fastening are reliable, strong and lightweight. Ratchets are sturdy, allow easy adjustment on the move, and provide a very firm hold on your foot. BOA is the lightest system available, and the lacing avoids uncomfortable contact points that can occur with some strap systems.