Not sure why you ask this question. Good quality sky replacement has been around for years in PS and many other editing programs. Perhaps the question is whether it is now too easy?
As far as this example goes, for me the replacement sky colours clash with the scene and there's a suggestion of a halo at the RH side, so without knowing whether that was due to the software or to its implementation, the answer is "don't know".
I have been doing sky replacements / enhancements for years, prior to this improved functionality. I find that I still have to spend time tweaking the output to get a believable looking sky, especially when dealing with problematic boundaries between the sky and the rest of the scene.
The replaced sky has to look like it belongs in the scene, so I tend to look for densities, hues and textures that make sense. The sky colour and the light of your example do not work well with the rest of the scene.
Thank you everyone for the comments
I guess the 'spectacular' option was a bit too much!
Warning!!!
I have many photographs with the sky replaced and never bother mentioning it when showing the photographs. Showed a coastal scene to a keen photographer acquaintance of mine and he immediately told me the sky I put in looked dramatic. However he laughed, then pointed out that the particular cloud formation was specific to a weather pattern caused by some mountains over 800 km away from my scene. He happened to be a senior meteorological scientist at The National Institute of Water and Atmospheric Research. Never had anyone else spot a substitute sky and he promised not tell on me...
One of the main things that I look for when replacing the sky is the angle of the sun and I try to match that with the shadows on the clouds. In the above image of the Haga Sophia gate, the foreground shadows indicate that the sunlight is coming from image right, with the shadows falling to image left. The shadows in the clouds also appear to me to be towards the image left.