I interviewed in the first few months of Aviate and was given a TBNT along with countless others. Aviate is, unfortunately, one and done so unless the stars align and I get another chance off the street, I'm done with UA, though I still fly their passengers safely every day.
I didn't prep because the Aviate documentation suggested this is not expected or warranted. Because UA HR elects not to disclose why they did not select me I have no idea what I did wrong and therefore no realistic chance to identify and correct any weaknesses.
I recently had the pleasure of flying on the line with a couple mainline guys who came back to my regional while on a COLA, and I just recently had a mainline FO as my seat support in training for upgrade. Got accolades from all of them and even managed to pick up an unsolicited recommendation from the examiner for a training department position before I got out of the sim. Yet UA said no to me.
One of the mainline guys asked if I was going to UA and I had to tell him what happened. He admitted UA HR got their hand slapped for the excessive number of TBNTs during the early days of Aviate. I only wish that came with another chance to interview. Guess I'm going to a LCC or, if I can pick up that LCA credential, the place with the double-breasted suits. Would have been nice to hang out with you guys...
My advice is to prep if you think it will help, but from my perspective it's all a roll of the dice....and I rolled snake eyes.