In seven years of playing Reach, it never even occurred to me that the knife would actually be used in game. Aside from most but not all assassination animations, knives, which are included on every chest armor, never factor into the game. That Bungie would have created a one-off animation for the small percentage of players that a) bought that armor and b) equipped it seems like an unlikely expectation. Plus that huge machete/kukri thing flopping around on my right shoulder always looked ridiculous to me anyway.
In my 8 years of playing reach, I never realized all of the chest armor variants had knives. Quite frankly once I found out none of them had any effects whatsoever I completely disregarded them since they were useless.
Why wouldn’t one expect something tangible? In my example, this particular piece would make a successful assassination attempt more likely thereby increasing the likelihood of increasing the appropriate commendation. Other effects I can think of off the top of my head - the Tacpad could slightly increase the range of the motion detector, the health pack could be used once per game(not spawn as that seems too OP), the shotgun and sniper ammo pieces could also be used once per game, and the chest piece with the robot arm could do slightly more damage in melee.
I quickly learned during the beta that the handicap settings were going to be detrimental to gameplay, so once the final release showed up I figured the armory would somehow offer defenses against them. Say - and I’m just throwing these out there - the thunderstorm effect would negate the close-range EMP of armor lock, the gungnir helmet would slightly accentuate camo-users so they are more easily seen, and a different helmet would protect against shots from above by jetpackers.