A low-ish Tier 3.
The Tier, however, does not indicate anything such as, for example, how fun it is to play the class, actual power level (power actually varies massively inside a Tier), or how worth it it is to actually take levels in the class.
Basically, this class only gets one unique "trick", and everything else it gets can be duplicated by other classes. It's like how the Fighter is pretty much the template they used for martial classes, or how Monks can be easily duplicated with a few magic items, some feats, and maybe a couple of level dips, or how you can pretty much copy everything a Barbarian can do with a single magic item and some class features you pick up over your levels.