Firstly, I want to state that I VERY rarely think a "full" class is ever needed. That's what archetypes are for. There's no reason this couldn't have been a very well crafted archetype for Warlock (mirror patron) or Wizard (a specialized illusionist) or even Bard or Sorcerer (using Inspiration or Sorcererous points for reflection points). It would, of course, be a smaller set of abilities but I think a small focused archetype is better than even the most well intentioned full class. I also think the Wisdom AND Constitution saving throw proficiencies were a bad choice, with both of those being the most useful of the saving throws where every other class gets a "good" and "bad" save. I also think summoning the reflection at the first level and front-loaded nature of the class makes it way too easy to take as a dip.
That being said, the class isn't bad in the Wizards of the Coast definition of "Over Powered". To WOTC, a class is OP if it takes fun away from any other player at the table (DM included) and I don't think this qualifies for that definition. If you were allowing this at your table, it would probably be a very interesting character to have playing. A half-caster that also is a decent combatant, the Reflectionist allows the player to summon a mirror duplicate which will be used with a variety of the abilities possesed by the reflectionist. The archetypes are all unique, with no overlap so if you're not worried about optimizers in your group, give the class a whirl. It will very very likely end up being fun!
I'll judge the class and award it stars based on what it is, not what it isn't. I'm going to give it a 4/5, taking one point away because of the front-loaded nature combined with the two awesome saving throws. If it was one or the other, it wouldn't be a big deal but both together is just a little too far against WOTC design for my tastes.
[4 of 5 Stars!]