Nightblade Tanks (Aka NBs) are rather an unpopular choice of Tank in The Elder Scrolls Online. The reason for this is because the NB offers no real unique group benefit, every buff/debuff applied by the NB can be obtain by some other source. Nightblades have a class passive buff, however this is only useful to Stamina Damage Dealers and it would be highly unlikely to see a group without another Nightblade who could apply the group buff more easily. The good thing about Nightblades Tanks is their damage mitigation, which is superior to other classes and one of the main reason you might choose a NB Tank. The NB has really good healing but no burst heal. You have to heal by combining a range of different healing skills that heal large chunks of health over time. Sustain for the NB is also very good but you will need to be an experienced player to benefit from this. Inexperienced players using a NB Tank will have a hard time to sustain, this is because you use skills that give you Magicka and Stamina when you do Light and Heavy Attacks, and for a inexperienced player this is much harder to do when you are not sure when its safe to do those Light and Heavy Attacks. NB’s struggle in Crowd Control situations as they don’t have a Magicka/Class based pull/chain and their CC is a skill that fears enemies, this is not very useful as enemies are CC immune after being pulled and cant be feared.
In the current game meta there is no real use for the NB Tank. You should try them out however just for the fun of playing a more challenging Tank class if that is something you enjoy doing!