Full Face masks. I bought them hoping they'd be the greatest thing ever. Talking to my wife while diving rather than fooling with handsigns? Awesome! Free classes with the purchase at a LDS. We used them exclusively for about 18 months (about 40 dives) before giving up. Never could get my air consumption anywhere near where it was with a normal regulator. We got tired of being the first people back on the boat, even when there were noob divers. We decided to switch back to regular mask/regulators (scubapro s600, not that the specific model matters much). I just stumbled on the receipt for them last week ($1,800.00 for two masks plus comms!). She wants to sell, I just can't bring myself to do it.. so they continue to sit in my dive closet.
Dive Knife It was something I never used, but frequently replaced after finding it had fallen out of the sheath. Replaced with a Trilobyte eezycut and "trauma" shears.
Trilobyte eezycut The trilobyte worked okay but it's got a metal blade. Eventually the blade rusts, so it looks bad and requires maintenance every few years. After the free blades were used up, I wasn't about to buy another given that there is a better option: Replaced with a
DGX sharpcut which has a ceramic blade. Mine's only 3 years old (2 years longer than a trilobyte blade lasts) but so far it is still sharp and there's no metal to rust.