Overall, my experience with Vander Altona after obtaining my keys was great. The room was excellent for the price. However, the experience leading up to check-in was difficult.
I booked my trip a few weeks in advance. Shortly thereafter, Vander emailed me a payment link to pay for my stay even though I provided a credit card to Hotels.com as part of the reservation. Hotels.com explicitly says to never pay through a payment link sent by the hotel and to only ever pay through Hotels.com's website. Vander also told me to provide them with my contact information. Hotels.com doesn't seem to allow this, so Vander told me how to avoid Hotels.com's automatic censorship of personal information (e.g., by adding spaces to my email address).
I initially ignored Vander's email since it seemed sketchy, and I didn't hear anything further from them. The day of my trip, I clicked on the reservation details and discovered that Vander had canceled my booking weeks prior (presumably because I didn't click their payment link). I never received any notification from Hotels.com or Vander.
I didn't have many other options on such short notice, so I re-booked with Vander and paid them through their link this time. It worked out fine.
Check-in was difficult as others have stated. The app didn't work. I called and was buzzed in, so no trouble in the end. But still--if you're going to have a no-staff-on-site model, it isn't really acceptable to not have a functioning app.