Your guide is whack, you already lost the game by picking nautilus.

He has so many weaknesses and draw backs that it doesn't matter if you can clear or not.

He can't really gank well at lvl 3 and not get behind.

He can't continually clear fast enough, and is extremely weak if he gets caught farming due to the reliance on his shield and its pretty long CD.

He may have great ganking potential, but lacks mobility to influence a majority of the map. Aside from that he is extremely weak to counter ganks.

His objective control is also weak, he can tank a good part of the damage but is no threat on his own. This is also true when he is on his own. He should never get a solo kill unless the other person royally messed up or he is extremely fed.

I love naut, zac, and all other tank jungler, but a majority are useless. naut is extremely weak and susceptible, zac is the same. neither really has the damage or tankiness to effect the game much before it is already decided.

Amumu is the best "tank" jungle and really the only one that should be used. I say "tank" because he should be build with AP, just so he deals damage. If an AP amumu gets a good bandage toss and ult off it is farm more game changing than a full tank amumu. There is no true tank that really fits in the jungle.

saying naut is good is rediculous, he is a better support than jungler at this point. j4, vi, lee, udyr, panth, sej, rek'sai, yi, ww, and many others are better than naut in the jungle. There is no need to cripple your team by playing him.

the reality comes down to naut being entirely defined by his shield. It is feast or famine with it, if it is up and the enemy team can't cut through it he is good, if they can burst it he is useless.

With all this said, he isn't terrible because many people don't know how to play against him and exploit his weaknesses. He also scales well and is one of the best peeling tanks in the game, but with assassins at their current lvl and all the burst damage flying around he is basically a niche pick.

He DOes need to be looked at, zac as well, not because they are terrible but build paths, itemization, and their ability to fulfill their role is greatly dimished since s3. Changes since s3 and s4 have finally culminated in the death of tanks in s5, it is about time they looked at it.