They work well enough, but to be honest they're really stock standard. Probably particularly unhelpful that they're MMD designs, so you have to use what you have-- leading to boring and/or cryptonesque outfits.
I'm personally particularly unfond of the outfits, though I like Alex's base design well enough (...which, when I look at it, is really just the fact that he has long green hair that gets a bit messy at the bottom due to the undetailed faces of this modeller). It's cute. I just think that the outfit could stand to be... more elaborate or original. In any way that conveys his general personality.
Also, the color scheme is nice.
Alexandra's design is really... It really looks too much like miku. You even drew her design in what is essentially Miku's pose.
Um. Yeah, the issue I'm seeing repeated most here is the taking of the KEI Crypton design quirks. This is pretty unoriginal and after five or so years of miku being released... it's really getting old seeing this. It would be pretty hard to make a KEICrypton designed UTAU appeal to a lot of people these days (unfortunately, including me. It's a really quick turn off).
Sorry if I'm being super short or rude it's pretty late where I live and its been a bit of a long day, and I swear to you I don't mean it in a bad way. I just want your design to be unique and appealing.