I was beating on it with my spanner repeatedly, somehow keeping its health up as we were hit with Flak. I told my friend, a fellow Engineer, to get the engines while I get the hull. -snip- within a few seconds after that initial mallet strike, our armor was gone and we didn't have time to repair it before we blew up.
The spanner heals a small amount of HP, but also has a low cooldown. With both of these in mind, the overall health repair rate is 20 a second.
The mallet heals a large amount of HP, but also has a high cooldown. With both of these in mind, the overall health repair rate is 25 a second.
This means that out of all the current tools, the mallet has the most bang for its buck repair/time-wise. If one was to match the cooldowns of the spanner to the mallet, they would see that 9 seconds of mallet repair is 225hp, and 9 seconds of spanner repair is 180hp(The spanner works in a cooldown of two, though, so this is purely objective- if the engineer was repairing constantly, they would technically get the extra hit in at 8 seconds, so at 9 seconds, the system would be on cooldown for one more second. If this was the case, it would be repaired to 200hp, which is still less than the mallet. Over a long period of time, that extra second of cooldown would make the mallet pull farther ahead by an extra 20 hp at 18 seconds, and so on).
The best time to use the 'weaker' tools is when the system simply doesn't need that much HP. If a hull is at about 99% of its maximum health, it is pointless to use the mallet on it. This would repair it to 100%, but also apply the 9 second cooldown. If the spanner was used instead, the system would be at 100%, but have a much shorter cooldown, and would allow for more repairs in quicker succession in the case that the system is hit again within 9 seconds.
If the system is at 10% health, the mallet will give an instantaneous burst to bring the system up to... lets just say 50% health. This burst may make the system survive the enemy's weapon volley; all that remains is to let the cooldown run for the next mallet whack- it healed more than all of the other tools could in that time span, so nothing more or different could have been done to out-repair the damage it sustained if the system breaks. If the spanner was used, it would simply patch up the damage that was applied, and could even lead to the system breaking before 9 seconds even passes. The spanner isn't as effective as the mallet as a long-term repair method.
-Edited a lot because I'm a grammar Nazi-