Kaylee's apartment was really excellent, and I highly recommend it for single travellers or couples. It suited my needs perfectly, and was a very well equipped, clean, tidy, and very homely little place to stay for a few days.
The location is excellent, being right in the heart of Vienna, yet peaceful and quiet at the same time. It's just a 3 minute walk to the WUK cultural centre for concerts and exhibitions (highly recommended !!), or about a 30 minute walk to the major museums and old town tourist attractions. There are several cafes and an excellent Spar supermarket (also highly recommended) within just a few minutes walk as well.
As other reviewers have mentioned, there are several flights of stairs to be ascended in order to reach the apartment, and there is no lift. I wasn't particularly bothered by this, and most seasoned travellers wouldn't be, but if you have any mobility problems or are not in the best of health or fitness, then sadly this apartment would probably not be for you, which would be a shame really.
Some people might also prefer an apartment with air conditioning. Again, I wasn't terribly bothered by this, and found the combination of open windows and the oscillating fan in the bedroom to be perfectly adequate to enable me to sleep in comfort, even though the temperature in the apartment when I visited in mid June never actually dropped below 26 degrees C.
The apartment is also quite small, and strictly suitable for no more than 2 people. Again, this was perfect for my needs as a lone traveller, and provided me with a very comfortable home for a few days. I'm sure couples would love it too.
I have to say that the check-in and check-out arrangements are really excellent. The whole thing is automated, and in fact I never even met Kaylee. She simply sends you two codes the day before you arrive. One you enter on the keypad at street level to access the building, and the second you then enter on a second keypad to enter the apartment. It works brilliantly and is very easy to use. Checking out is as simple as walking out the door and pressing a button. That's it ! It's just like coming home to one's own apartment in Vienna. Really fabulous in that respect.
I would certainly book this apartment again for any future visit to Vienna, and would find it perfectly suitable for any stay of up to say one week in duration.
I also recommend using the AirportDriver.at taxi service. I pre-booked both my inbound and outbound airport transfers, at 38 Euros each way (in June 2022) and found the service to be really excellent.
Even though my inbound flight was delayed by 3 hours the driver was sitting waiting for me in the arrivals hall, and was not remotely bothered by my late arrival ! The journey to Kaylee's apartment takes around 25 minutes. On the return journey the driver even arrived 20 minutes early just in case I wanted to get going a bit sooner than planned (how good is that ?!!). It really was an excellent service, and I would definitely use AirportDriver.at again. You can even pay by card/ApplePay in the car without needing to bother with cash.
So overall, I'm very happy to recommend Kaylee's "Mellow Yellow" apartment on Sobieskigasse for short stays in Vienna for lone travellers or couples.