I bought a small torque wrench and accessories for use on my bikes. After using it for a while, I decided it's usually unnecessary. Allen wrenches are sized, like most wrenches, to be a proper length for the size of the fastener. Try putting to much torque on one, and you'll feel it stabbing you. When in doubt, a torque wrench can be helpful. I used to set a minimum torque with torque wrench, then snug slightly with a hand held Allen key just to verify that going by feel is accurate enough. For higher torques, a torque wrench is more important, I find.