REASONS TO BUY
Simple
Fun to place
Inexpensive
Great in pockets
REASONS TO AVOID
Limited applications
Walk easily unless placed in tight spots in which case they are tricky to clean
- they use dyneema instead of nylon that is slightly stronger
- they are annodized
- they are only available in four sizes (nylon tricams available in 14 sizes)
- they are $1 more expensive
Tricams offer protection in shallow pocketed placements. Occasionally that is in granite but usually it occurs in limestone or other pocketed rock. Tricams have a strong following from old school climbers.
I don't consider them mandatory for any Yosemite or sandstone routes, but climber in more pocketed areas often swear by them. That said, usually a cam with a flexible stem and narrow head will work in a tricam placement.